PyImportSortBear.py: passing known_third_party to isort_settings

known_third_party_imports was being passed to the run fucntion but it was not being
passed to the wrapper function isort_settings. This update fixes the issue.

Fixes #1510

Author: madhukar01

bears/python/PyImportSortBear.py

@@ -169,6 +169,7 @@ def run(self, filename, file,
             forced_separate=forced_separate_imports,
             multi_line_output=isort_multi_line_output,
             known_first_party=known_first_party_imports,
+            known_third_party=known_third_party_imports,
             line_length=max_line_length,
             force_to_top=imports_forced_to_top)