bad indent with cython

[jiajunhuang]

cdef void foo(
        i
)

but not

cdef void foo(
    i
)

[blueyed]

/cc @anntzer (via #48)

[anntzer]

This is not different from regular python indents, which this plugin also sets to

def foo(
        i
): ...

(i.e., 8 spaces) in order to avoid having the same indent as the block below.

Now it is correct that Cython has both the form with a final colon (as in Python) and without (i.e., a function declaration, similar to typehint stub files), but when the indent is made we don't know yet what the user is going to do, so defaulting to 8 spaces seems good enough.