Log Message:
Update ruby-simplecov to 0.15.0.

0.15.0 (2017-08-14) \ 
([changes](https://github.com/colszowka/simplecov/compare/v0.14.1...v0.15.0))
=======

## Enhancements

* Ability to use regex filters for removing files from the output. See \ 
[#589](https://github.com/colszowka/simplecov/pull/589) (thanks @jsteel)

## Bugfixes

* Fix merging race condition when running tests in parallel and merging
  them. See [#570](https://github.com/colszowka/simplecov/pull/570) (thanks
  @jenseng)
* Fix relevant lines for unloaded files - comments, skipped code etc. are
  correctly classigied as irrelevant. See
  [#605](https://github.com/colszowka/simplecov/pull/605) (thanks @odlp)
* Allow using simplecov with frozen-string-literals enabled. See
  [#590](https://github.com/colszowka/simplecov/pull/590) (thanks @pat)
* Make sure Array Filter can use all other filter types. See
  [#589](https://github.com/colszowka/simplecov/pull/589) (thanks @jsteel)
* Make sure file names use `Simplecov.root` as base avoiding using full
  absolute project paths. See
  [#589](https://github.com/colszowka/simplecov/pull/589) (thanks @jsteel)