PARQUET-150 Update merge script issue id matching.

This matches a word boundary after the issue id rather than a colon.

Author: Ryan Blue <blue@apache.org>

This patch had conflicts when merged, resolved by
Committer: Ryan Blue <blue@apache.org>

Closes #94 from rdblue/PARQUET-150-update-merge-script and squashes the following commits:

cc39713 [Ryan Blue] PARQUET-150: Update merge script issue id matching.