Fix a typo in WKT's test suite

Hi!
Sorry for bothering with such a minor thing, but I just noticed and fixed one annoying typo in WKT's test suite:
`"accpets" -> "accepts"`

Thanks!

python/google/protobuf/internal/well_known_types_test.py

@@ -101,7 +101,7 @@ class TimeUtilTest(TimeUtilTestBase):
     message.FromJsonString('1970-01-01T00:00:00.1Z')
     self.assertEqual(0, message.seconds)
     self.assertEqual(100000000, message.nanos)
-    # Parsing accpets offsets.
+    # Parsing accepts offsets.
     message.FromJsonString('1970-01-01T00:00:00-08:00')
     self.assertEqual(8 * 3600, message.seconds)
     self.assertEqual(0, message.nanos)