Bump pep8 from 1.5.6 to 1.5.7

Bump pep8 version in an overlapping way, so add pep8 version 1.5.7 and a
subsequent patch will drop pep8 1.5.6.

Pep8 1.5.7 has additional bug fixes

Change-Id: Ic356886984f70992276b49555e1ec7b3d34b000a
Merge "Bump pep8 from 1.5.6 to 1.5.7"