Log Message:
security/ruby-sshkit: update to 1.16.0

## [1.16.0][] (2018-02-03)

  * [#417](https://github.com/capistrano/sshkit/pull/417): Cache key generation \ 
for connections becomes slow when `known_hosts` is a valid `net/ssh` options and \ 
`known_hosts` file is big. This changes the cache key generation and fixes \ 
performance issue - [@ElvinEfendi](https://github.com/ElvinEfendi).
## [1.15.1][] (2017-11-18)

This is a small bug-fix release that fixes problems with `upload!` and \ 
`download!` that were inadvertently introduced in 1.15.0.

### Breaking changes

  * None

### Bug fixes

  * [#410](https://github.com/capistrano/sshkit/pull/410): fix NoMethodError \ 
when using upload!/download! with Pathnames - \ 
[@UnderpantsGnome](https://github.com/UnderpantsGnome)
  * [#411](https://github.com/capistrano/sshkit/pull/410): fix upload!/download! \ 
when using relative paths outside of `within` blocks -  \ 
[@Fjan](https://github.com/Fjan)

## [1.15.0][] (2017-11-03)

### New features

  * [#408](https://github.com/capistrano/sshkit/pull/408): upload! and download! \ 
now respect `within` - [@sj26](https://github.com/sj26)

### Potentially breaking changes

  * `upload!` and `download!` now support remote paths which are
    relative to the `within` working directory. They were previously documented
    as only supporting absolute paths, but relative paths still worked relative
    to the remote working directory. If you rely on the previous behaviour you
    may need to adjust your code.