Mention Bug Fix in release notes

When interrupting Git processes in Git Bash by
pressing Ctrl+C, [Git now removes `.lock` files as
designed](git-for-windows/msys2-runtime#15)
([accompanying Git
PR](git-for-windows/git#1170); this should also
fix [issue #338](git-for-windows/git#338)).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

ReleaseNotes.md

@@ -43,6 +43,7 @@ This package contains software from a number of other projects including Bash, z
 ### Bug Fixes
 
 * The documentation of Git for Windows' several config files [was improved](https://github.com/git-for-windows/git/pull/1165).
+* When interrupting Git processes in Git Bash by pressing Ctrl+C, [Git now removes `.lock` files as designed](https://github.com/git-for-windows/msys2-runtime/pull/15) ([accompanying Git PR](https://github.com/git-for-windows/git/pull/1170); this should also fix [issue #338](https://github.com/git-for-windows/git/issues/338)).
 
 ## Changes since Git for Windows v2.12.2(2) (April 5th 2017)