Change unicode() —> six.text_type() for Python 3 (google#128)

See google#111

Author: cclauss

fire/parser_fuzz_test.py

@@ -68,8 +68,8 @@ def testDefaultParseValueFuzz(self, value):
       raise
 
     try:
-      uvalue = unicode(value)
-      uresult = unicode(result)
+      uvalue = six.text_type(value)
+      uresult = six.text_type(result)
     except UnicodeDecodeError:
       # This is not what we're testing.
       return