Update to a newer hacking library
The older hacking library has a cap on pbr <2.0, with the recent 2.0.0
release of PBR it's causing failures in the pep8 job. hacking isn't
kept in sync via the typical proposal-bot updates. Do it manually to
clear the gate issue.
Related-Bug:
# process, which may cause wedges in the gate later.
coverage>=4.0 # Apache-2.0
fixtures>=3.0.0 # Apache-2.0/BSD
-hacking<0.11,>=0.10.0
+hacking>=0.12.0,!=0.13.0,<0.14 # Apache-2.0
mock>=2.0 # BSD
python-subunit>=0.0.18 # Apache-2.0/BSD
sphinx>=1.5.1 # BSD
