fix compiler warning

Author: benjaminp

Grammar/Grammar

@@ -24,7 +24,8 @@ decorators: decorator+
 decorated: decorators (classdef | funcdef)
 funcdef: 'def' NAME parameters ['->' test] ':' suite
 parameters: '(' [typedargslist] ')'
-typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [','
+typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])*
+               [',' '/' (',' tfpdef ['=' test])*] [','
        ['*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef]]
      |  '*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef)
 tfpdef: NAME [':' test]