Log Message:
Update ruby-bundler to 1.15.1.

## 1.15.1 (2017-06-02)

Bugfixes:

  - `bundle lock --update GEM` will fail gracefully when the gem is not in the \ 
lockfile (#5693, @segiddins)
  - `bundle init --gemspec` will fail gracefully when the gemspec is invalid \ 
(@colby-swandale)
  - `bundle install --force` works when the gemfile contains git gems (#5678, \ 
@segiddins)
  - `bundle env` will print well-formed markdown when there are no settings \ 
(#5677, @segiddins)

## 1.15.0 (2017-05-19)

This space intentionally left blank.

## 1.15.0.pre.4 (2017-05-10)

Bugfixes:

  - avoid conflicts when `Gem.finish_resolve` is called after the bundle has \ 
been set up (@segiddins)
  - ensure that `Gem::Specification.find_by_name` always returns an object that \ 
can have `#to_spec` called on it (#5592, @jules2689)

## 1.15.0.pre.3 (2017-04-30)

Bugfixes:

  - avoid redundant blank lines in the readme generated by `bundle gem` (@koic)
  - ensure that `open-uri` is not loaded after `bundle exec` (@segiddins)
  - print a helpful error message when an activated default gem conflicts with
    a gem in the gemfile (@segiddins)
  - only shorten `ref` option for git gems when it is a SHA (#5620, @segiddins)

## 1.15.0.pre.2 (2017-04-23)

Bugfixes:

  - ensure pre-existing fit caches are updated from remote sources (#5423, \ 
@alextaylor000)
  - avoid duplicating specs in the lockfile after updating with the gem \ 
uninstalled (#5599, @segiddins)
  - ensure git gems have their extensions available at runtime (#5594, \ 
@jules2689, @segiddins)

## 1.15.0.pre.1 (2017-04-16)

Features:

  - print a notification when a newer version of bundler is available (#4683, \ 
@segiddins)
  - add man pages for all bundler commands (#4988, @feministy)
  - add the `bundle info` command (@fredrb, @colby-swandale)
  - all files created with `bundle gem` comply with the bundler style guide \ 
(@zachahn)
  - if installing a gem fails, print out the reason the gem needed to be \ 
installed (#5078, @segiddins)
  - allow setting `gem.push_key` to set the key used when running `rake release` \ 
(@DTrierweiler)
  - print gem versions that are regressing during `bundle update` in yellow \ 
(#5506, @brchristian)
  - avoid printing extraneous dependencies when the resolver encounters a \ 
conflict (@segiddins)
  - add the `bundle issue` command that prints instructions for reporting issues \ 
(#4871, @jonathanpike)
  - add `--source` and `--group` options to the `bundle inject` command (#5452, \ 
@Shekharrajak)
  - add the `bundle add` command to add a gem to the gemfile (@denniss)
  - add the `bundle pristine` command to re-install gems from cached `.gem` \ 
files (#4509, @denniss)
  - add a `--parseable` option for `bundle config` (@JuanitoFatas, @colby-swandale)

Performance:

  - speed up gemfile initialization by storing locked dependencies as a hash \ 
(@jules2689)
  - speed up gemfile initialization by making locked dependency comparison lazy, \ 
avoiding object allocation (@jules2689)
  - only validate git gems when they are downloaded, instead of every time \ 
`Bundler.setup` is run (@segiddins)
  - avoid regenerating the lockfile when nothing has changed (@segiddins)
  - avoid diffing large arrays when no sources in the gemfile have changed \ 
(@segiddins)
  - avoid evaluating full gemspecs when running with RubyGems 2.5+ (@segiddins)

Bugfixes:

  - fix cases where `bundle update` would print a resolver conflict instead of \ 
updating the selected gems (#5031, #5095, @segiddins)
  - print out a stack trace after an interrupt when running in debug mode \ 
(@segiddins)
  - print out when bundler starts fetching a gem from a remote server (@segiddins)
  - fix `bundle gem` failing when `git` is unavailable (#5458, @Shekharrajak, \ 
@colby-swandale)
  - suggest the appropriate command to unfreeze a bundle (#5009, @denniss)
  - ensure nested calls to `bundle exec` resolve default gems correctly (#5500, \ 
@segiddins)
  - ensure that a plugin failing to install doesn't uninstall other plugins \ 
(@kerrizor, @roseaboveit)
  - ensure `socket` is required before being referenced (#5533, @rafaelfranca)
  - allow running `bundle outdated` when gems aren't installed locally (#5553, \ 
@segiddins)
  - print a helpful error when `bundle exec`ing to a gem that isn't included in \ 
the bundle (#5487, @segiddins)
  - print an error message when a non-git gem is given a `branch` option (#5530, \ 
@colby-swandale)
  - allow interrupts to exit the process after gems have been installed (@segiddins)
  - print the underlying error when downloading gem metadata fails (#5579, \ 
@segiddins)
  - avoid deadlocking when installing with a lockfile that is missing \ 
dependencies (#5378, #5480, #5519, #5526, #5529, #5549, #5572, @segiddins)