Upgrade hooks

[asottile]

quite a bit of stuff here:

• black learned about slices
• black changed its mind on some reflows

[asottile]

hmmmmmm! I'll have to look at this some more

[asottile]

there's a bit of an edge case with the % format rewriting that I hadn't noticed in my own code (as I liberally use unicode_literals):

>>> '%s' % (u'\u2603')
u'\u2603'
>>> '{}'.format(u'\u2603')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2603' in position 0: ordinal not in range(128)

going to save that for a separate branch since that bit is riskier and just do black and such

[asottile]

Hah black changed what line the code ends up on breaking the test. I'll fix this when I'm at a computer

[coveralls]

Coverage increased (+0.05%) to 92.677% when pulling 1c49e52 on asottile:upgrade_hooks into 42b3125 on pytest-dev:master.

[RonnyPfannschmidt]

i skimmed the changes and overall its getting much better - @ambv is doing a great job with getting blacks more awesome

[RonnyPfannschmidt]

should i sort out the conflict my other merge triggered or do we leave it for later

[asottile]

I can reapply pretty easily