Addressing a handful of lint issues.

[reinecke]

Somehow lint started failing for people on a lot of their branches due to issues in master, here is one such example: https://travis-ci.com/github/PixarAnimationStudios/OpenTimelineIO/jobs/333466701

Worth noting, there was one function in the kdenlive adapter I didn't know the correct fix for so I just muted the warning. This is likely broken and will require someone with more experience in that realm to address:

def write_keyframes(kfdict):
    """Build a MLT keyframe string"""
    # TODO: The following line is causing a lint error:
    #       F524 '...'.format(...) is missing argument(s) for placeholder(s): 1
    # This will likely cause an exception at runtime and should be addressed.
    return ';'.join('{}={}'.format(str(int(t.value))).format(v)  # noqa: F524
                    for t, v in kfdict.items())

[meshula]

Everything looks fine, although I think the format line should be addressed, as my read of what is intended there suggests to (non-python guru) me that it's actually incorrect as opposed to merely annoying the linter.

[ssteinbach]

Looks good to me, thanks for cleaning this up.

[reinecke]

After discussion, going ahead and merging despite the unaddressed issue in the kdenlive adapter, filed issue as #703 instead.