Allow .fixture.js(x) files to have lines >80 chars.

Summary:
These files just hold test data, and it's not useful to make people
wrap the test data which could have really long strings in it.

Test Plan:
In webapp, I temporarily modified
   javascript/content-library-package/components/thumbnail.jsx.fixture.js
to remove the 'max-len' mention in the eslint-disable comment.  I then
ran
   ka-lint javascript/content-library-package/components/thumbnail.jsx.fixture.js
which ran without error.

Reviewers: kevinb, jlfwong

Reviewed By: jlfwong

Differential Revision: https://phabricator.khanacademy.org/D22500

linters.py

@@ -400,6 +400,11 @@ def _process_one_line(self, filename, output_line, contents_lines):
         if '@Nolint' in bad_line:
             return 0
 
+        # Allow long lines in fixture files, which just hold test data.
+        if (' Emax-len ' in output_line and
+                filename.endswith(('.fixture.js', 'fixture.jsx'))):
+            return 0
+
         print self._maybe_add_arc_fix(output_line, bad_line)
         return 1