trivial change to reset tip after branch close

Author: plinss

README.markdown

@@ -19,3 +19,4 @@ both PRs will be merged at the same time. Note that a test change that contradic
 not be merged before the corresponding spec change. If testing is not practical, please explain why
 and if appropriate [file an issue](https://github.com/w3c/web-platform-tests/issues/new) to follow
 up later. Add the `type:untestable` or `type:missing-coverage` label as appropriate.
+