Mention Bug Fix in release notes

Git GUI [now sets author information correctly when
amending](git-for-windows/git#726).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

installer/ReleaseNotes.md

@@ -38,6 +38,7 @@ This package contains software from a number of other projects including Bash, z
 
 * FSCache [is now enabled by default](https://github.com/git-for-windows/build-extra/commit/a1ae146) even when upgrading from previous Git for Windows versions.
 * We now add `git.exe` to the `PATH` [by default](https://github.com/git-for-windows/build-extra/commit/1e2e00e) even when upgrading from previous Git for Windows versions.
+* Git GUI [now sets author information correctly when amending](https://github.com/git-for-windows/git/pull/726).
 
 ## Changes since Git for Windows v2.8.0 (March 29th 2016)