Fix multi-token type hints in line formatter

[jakebailey]

The line formatter handles the spacing of = inside of a function declaration with a type hint by looking two tokens behind the = to see if there's a colon. This works for simple declarations like def foo(a: str = "bar"), but does not work for more complicated types such as def foo(a: Union[int, str] = "bar").

A more correct method would be to look for a colon anywhere behind the = until reaching a ( or ,.

[jakebailey]

This is unfortunately not as simple as I originally thought, since you'd reach the comma in Union[int, str] before hitting the colon and then choose not to add spacing.

[jakebailey]

Fixed in #168.