Correct a typo in test_sourcecode.py

Author: felixonmars

tests/test_sourcecode.py

@@ -19,7 +19,7 @@ def test_flake8(self):
         try:
             import flake8  # NoQA
         except ImportError:
-            raise unittest.SkipTest('flake8 moudule is missing')
+            raise unittest.SkipTest('flake8 module is missing')
 
         for subdir in ['examples', 'uvloop', 'tests']:
             try: