Version bump for v1.6.1.0 (fixes #99)

changelog.md

 # Changelog for [`process` package](http://hackage.haskell.org/package/process)
 
-## Unreleased changes
+## 1.6.1.1 *July 2017*
 
 * Expose `CGid`, `GroupID`, and `UserID` from `System.Process.Internals`
   [#90](https://github.com/haskell/process/issues/90)

process.cabal

 name:          process
-version:       1.6.0.0
+version:       1.6.1.0
 -- NOTE: Don't forget to update ./changelog.md
 license:       BSD3
 license-file:  LICENSE