Update ruby-sshkit to 1.6.1.

## 1.6.0

  * Fix colorize to use the correct API (@fazibear)
  * Lock colorize (sorry guys) version at >= 0.7.0

## 1.6.0 (Yanked, because of colorize.)

  * Force dependency on colorize v0.6.0
  * Add your entries here, remember to credit yourself however you want to be
    credited!
  * Remove strip from capture to preserve whitespace. Nick Townsend
  * Add vmware_fusion Vagrant provider. Nick Townsend
  * Add some padding to the pretty log formatter

## 1.5.1

  * Use `sudo -u` rather than `sudo su` to switch users. Mat Trudel

## 1.5.0

  * Deprecate background helper - too many badly behaved pseudo-daemons. Lee Hambley
  * Don't colourize unless $stdout is a tty. Lee Hambley
  * Remove out of date "Known Issues" section from README. Lee Hambley
  * Dealy variable interpolation inside `as()` block. Nick Townsend
  * Fixes for functional tests under modern Vagrant. Lewis Marshal
  * Fixes for connection pooling. Chris Heald
  * Add `localhost` hostname to local backend. Adam Mckaig
  * Wrap execptions to include hostname. Brecht Hoflack
  * Remove `shellwords` stdlib dependency Bruno Sutic
  * Remove unused `cooldown` accessor. Bruno Sutic
  * Replace Term::ANSIColor with a lighter solution. Tom Clements
  * Documentation fixes. Matt Brictson

## 1.4.0

https://github.com/capistrano/sshkit/compare/v1.3.0...v1.4.0

  * Removed `invoke` alias for [`SSHKit::Backend::Printer.execute`](https://github.com/capistrano/sshkit/blob/master/lib/sshkit/backends/printer.rb#L20). This is to prevent collisions with
  methods in capistrano with similar names, and to provide a cleaner API. See [capistrano issue 912](https://github.com/capistrano/capistrano/issues/912) and [issue 107](https://github.com/capistrano/sshkit/issues/107) for more details.
  * Connection pooling now uses a thread local to store connection pool, giving each thread its own connection pool. Thank you @mbrictson see [#101](https://github.com/capistrano/sshkit/pull/101) for more.
  * Command map indifferent towards strings and symbols thanks to @thomasfedb see [#91](https://github.com/capistrano/sshkit/pull/91)
  * Moved vagrant wrapper to `support` directory, added ability to run tests with vagrant using ssh. @miry see [#64](https://github.com/capistrano/sshkit/pull/64)
  * Removed unnecessary require `require_relative '../sshkit'` in `lib/sshkit/dsl.rb` prevents warnings thanks @brabic.
  * Doc fixes thanks @seanhandley @vojto

(taca)