Fix up simple typo: invididual -> individual

python/google/protobuf/internal/_parameterized.py

@@ -51,7 +51,7 @@ like a normal test method, with its own setUp/tearDown cycle. In the
 example above, there are three separate testcases, one of which will
 fail due to an assertion error (1 + 1 != 3).
 
-Parameters for invididual test cases can be tuples (with positional parameters)
+Parameters for individual test cases can be tuples (with positional parameters)
 or dictionaries (with named parameters):
 
   class AdditionExample(parameterized.TestCase):