Fix contribution branching strategy (NuGet#8772)

CONTRIBUTING.md

@@ -16,9 +16,9 @@ A lot of the issues that arise in our tracker are things we'd like to do and wou
 1. Make sure there is an issue in the [Issue Tracker](https://github.com/NuGet/NuGetGallery/issues) for the feature or bug you want to fix. If not, create one!
   * **Pull Requests without an associated issue will not be accepted!**
 1. Create a fork in GitHub
-1. Create a branch off of the **master** branch. Name it something which easily links it back to the issue. For example: "Bug-1234".
+1. Create a branch off of the **dev** branch. Name it something which easily links it back to the issue. For example: "Bug-1234".
 1. Make your changes
-1. Send a Pull Request from your branch to the **master** branch.
+1. Send a Pull Request from your branch to the **dev** branch.
 
 If you mess up the branching or get confused, that's OK, we'd rather have your contribution than have you waste a lot of time figuring out our branches. However, using the right branches will help us immensely and will make it much easier for us to quickly accept your contribution!