Fix parse error when static class method comes after proto method

This fails to parse:
`class A { foo() {} static bar() {}}`

I'm not sure exactly why the strict branching check was put in place, but we
don't need to do much more than check if the first token is 'static' when
parsing a method definition -- so this works and fixes the issue.

All tests pass, etc

https://code.google.com/p/esprima/issues/detail?id=430