YapfBear: Disable syntax verification

Syntax verification is supposed to be a private feature in yapf, used
for debugging, but they're still defaulting its flag to True on the
public FormatFile function. We need to set it to False to disable
syntax error checking in yapf (which seems to be an unmaintained
feature of it, since it raises exceptions on async/await and Python 2's
print statement), see discussion at
google/yapf#293

Fixes #738

Author: underyx

bears/python/YapfBear.py

@@ -142,7 +142,8 @@ def run(self, filename, file,
         with prepare_file(options.splitlines(keepends=True),
                           None) as (file_, fname):
             corrected = FormatFile(filename,
-                                   style_config=fname)[0].splitlines(True)
+                                   style_config=fname,
+                                   verify=False)[0].splitlines(True)
         diffs = Diff.from_string_arrays(file, corrected).split_diff()
         for diff in diffs:
             yield Result(self,