lint-all: Soften check for % comprehensions.

tools/lint-all

@@ -347,7 +347,7 @@ def build_custom_checkers(by_lang):
         # This next check could have false positives, but it seems pretty
         # rare; if we find any, they can be added to the exclude list for
         # this rule.
-        {'pattern': '% [a-zA-Z0-9_.]*\)?$',
+        {'pattern': ' % [a-zA-Z0-9_.]*\)?$',
          'exclude_line': set([
              ('tools/tests/test_template_parser.py', '{% foo'),
          ]),