Fix unwanted spacing around equals in override completion

[jakebailey]

This resolves #145, but with the catch that LS seems to drop the type information before getting to the code I fixed, so repeating the example in #145 with the following base class:

class Foo:
    def bar(arg: int = 5):
        pass

Will complete out to:

class Bar(Foo):
    def bar(arg=5):
        return super().bar()

When it would be preferable to produce:

class Bar(Foo):
    def bar(arg: int = 5):
        return super().bar()

Making that improvement may take more investigation.