Use TRAVIS_BRANCH environment variable

Ref #713

travis/pr-check-base.py

@@ -1,11 +1,7 @@
-import json, os, sys
-if sys.version.startswith('2'):
-    from urllib2 import urlopen, HTTPError
-else:
-    from urllib.request import urlopen
-    from urllib.error import HTTPError
-try:
+import os, sys
 repo = os.environ.get('TRAVIS_REPO_SLUG', 'dfhack/dfhack').lower()
+branch = os.environ.get('TRAVIS_BRANCH', 'master')
+try:
     pr_id = int(os.environ.get('TRAVIS_PULL_REQUEST', 'false'))
 except ValueError:
     print('Not a pull request')
@@ -14,18 +10,7 @@ print('Pull request %s#%i' % (repo, pr_id))
 if repo != 'dfhack/dfhack':
     print('Not in dfhack/dfhack')
     sys.exit(0)
-res = {}
-try:
-    res = json.loads(urlopen('https://api.github.com/repos/%s/pulls/%i' % (repo, pr_id)).read().decode('utf-8'))
-except ValueError:
-    pass
-except HTTPError as e:
-    print('Failed to retrieve PR information from API: %s' % e)
-    sys.exit(2)
-if 'base' not in res or 'ref' not in res['base']:
-    print('Invalid JSON returned from API')
-    sys.exit(2)
-if res['base']['ref'] != 'develop':
+if branch != 'develop':
     print('Not based on develop branch')
     sys.exit(1)
 else: