Fix syntax error in compare_build_artifacts.py.

BUG=314403

Review-Url: https://codereview.chromium.org/2278813002
Cr-Commit-Position: refs/heads/master@{#414322}

tools/determinism/compare_build_artifacts.py

@@ -575,7 +575,7 @@ def main():
   target = {
       'darwin': 'mac', 'linux2': 'linux', 'win32': 'win'
   }.get(sys.platform, sys.platform)
-  parser.add_option('-t', '--target-platform', help='The target platform.'
+  parser.add_option('-t', '--target-platform', help='The target platform.',
                     default=target, choices=('android', 'mac', 'linux', 'win'))
   options, _ = parser.parse_args()