Pin up pep8 for compatibility with newest flake8.

Flake8 2.0 requires at least pep8 = 1.4.3.

@tisto This is required for running the translation report job on jenkins - the jenkins-code-analysis.cfg is not running at the moment.

The `./bin/jenkins-code-analysis-flake8` has some errors at the moment, but it has it with Flake8 1.x also so I did not investigate further. The error is:
```
-n Analyse packages/plonetheme/sunburst/
xargs: illegal option -- r
usage: xargs [-0opt] [-E eofstr] [-I replstr [-R replacements]] [-J replstr]
             [-L number] [-n number [-x]] [-P maxprocs] [-s size]
             [utility [argument ...]]
```