lint: Fix tools tests.

These were broken when Travis wasn't running properly.

tools/linter_lib/custom_check.py

@@ -598,7 +598,7 @@ def build_custom_checkers(by_lang):
          'description': 'Linkified markdown URLs should use cleaner <http://example.com> syntax.'},
         {'pattern': 'https://zulip.readthedocs.io/en/latest/[a-zA-Z0-9]',
          'exclude': ['docs/overview/contributing.md', 'docs/overview/readme-symlink.md'],
-         'include_only': set(['docs']),
+         'include_only': set(['docs/']),
          'description': "Use relatve links (../foo/bar.html) to other documents in docs/",
          },
         {'pattern': '\][(][^#h]',

tools/tests/test_linter_custom_check.py

@@ -17,7 +17,8 @@ class TestCustomRules(TestCase):
         # type: () -> None
         self.all_rules = []  # type: List[Dict[str, Any]]
         with patch('tools.linter_lib.custom_check.custom_check_file', return_value=False) as mock_custom_check_file:
-            by_lang = dict.fromkeys(['py', 'js', 'sh', 'css', 'handlebars', 'html', 'json', 'md', 'txt', 'text', 'yaml'],
+            by_lang = dict.fromkeys(['py', 'js', 'sh', 'css', 'handlebars', 'html',
+                                     'json', 'md', 'txt', 'text', 'yaml', 'rst'],
                                     ['foo/bar.baz'])
             check_custom_checks_py, check_custom_checks_nonpy = build_custom_checkers(by_lang)
             check_custom_checks_py()