fix style issues in pipe test

Author: megatron-me-uk

python/pyspark/tests.py

@@ -875,7 +875,7 @@ def test_sortByKey_uses_all_partitions_not_only_first_and_last(self):
                 self.assertGreater(size, 0)
 
     def test_pipe_functions(self):
-        data = ['1','2','3']
+        data = ['1', '2', '3']
         rdd = self.sc.parallelize(data)
         self.assertRaises(Exception, rdd.pipe('cc').collect())
         result = rdd.pipe('cat').collect().sort()