Mention Bug Fix in release notes

A bug which on occasion caused lengthy rebase
runs to crash without error message [was
fixed](git-for-windows/git#2182).

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

Author: dscho

ReleaseNotes.md

@@ -55,6 +55,7 @@ This package contains software from a number of other projects including Bash, z
 * `git update-git-for-windows` (i.e. the auto updater of Git for Windows) now [reports correctly when it failed to access the GitHub API](https://github.com/git-for-windows/build-extra/pull/239).
 * Git for Windows' updater [no longer runs into GitHub API rate limits](https://github.com/git-for-windows/build-extra/pull/242) (this used to be quite common in enterprise scenarios, where many users would share one IP as far as GitHub is concerned).
 * gitk [no longer fails with "filename too long"](https://github.com/git-for-windows/git/pull/2170) when there are 1,000+ branches/tags.
+* A bug which on occasion caused lengthy rebase runs to crash without error message [was fixed](https://github.com/git-for-windows/git/pull/2182).
 
 ## Changes since Git for Windows v2.20.1 (December 15th 2018)