Add #425 to changelog

Author: dahlbyk

CHANGELOG.md

@@ -8,6 +8,8 @@
   ([PR #422](https://github.com/dahlbyk/posh-git/pull/422))
 - `Add-PoshGitToProfile` will no longer modify a signed `$PROFILE` script; it also learned `-Confirm`
   ([PR #428](https://github.com/dahlbyk/posh-git/pull/428))
+- Overwrite pre-0.7 posh-git prompt on import
+  ([PR #425](https://github.com/dahlbyk/posh-git/pull/425))
 
 ## 0.7.0 - February 14, 2017
 This release has focused on improving the "getting started" experience by adding an `Add-PoshGitToProfile` command that