Fix a bug in test_get_grackle_version

Essentially, a bug made the test fail if you ran the test and you had
checked out the commit associated with the tag of the most recent
grackle version number.

Author: mabruzzo

src/python/tests/test_get_grackle_version.py

@@ -41,7 +41,7 @@ def _run(args):
     latest_tagged_version = most_recent_tag[len(prefix) :]
 
     # get the actual revision when most_recent tag was introduced
-    revision_of_tag = _run(["git", "rev-parse", "-n", "1", most_recent_tag])
+    revision_of_tag = _run(["git", "rev-list", "-n", "1", most_recent_tag])
 
     # get the branch name and current revision
     branch = _run(["git", "rev-parse", "--abbrev-ref", "HEAD"])