Mention New Feature in release notes

Comes with [patch level
5](git-for-windows/msys2-runtime@40af06a)
of the MSYS2 runtime (Git for Windows flavor) based on [Cygwin
2.9.0](https://cygwin.com/ml/cygwin-announce/2017-09/msg00056.html).

Signed-off-by: Git for Windows Build Agent <[email protected]>

Author: Git for Windows Build Agent

ReleaseNotes.md

@@ -44,6 +44,7 @@ Git for Windows now has a new homepage: [https://gitforwindows.org/](https://git
 * Comes with [OpenSSL v1.0.2n](https://www.openssl.org/news/openssl-1.0.2-notes.html).
 * `git checkout` [is now a lot faster when checking out a *lot* of files](https://github.com/git-for-windows/git/pull/1419).
 * The `core.excludesfile` [can now reference a symbolic link](https://github.com/git-for-windows/git/issues/1392).
+* Comes with [patch level 5](https://github.com/git-for-windows/msys2-runtime/commit/40af06afb9691cfa05a5eb99db42de82a19c3fc7) of the MSYS2 runtime (Git for Windows flavor) based on [Cygwin 2.9.0](https://cygwin.com/ml/cygwin-announce/2017-09/msg00056.html).
 
 ### Bug Fixes