fix requirement.txt format

you didn't tested your doc

```
pip install -r metricfactory/requirements.txt
https://github.com/Lacrymology/wishbone.git@graphite-pickle#egg=wishbone should either by a path to a local project or a VCS url beginning with svn+, git+, hg+, or bzr+
Storing complete log in /Users/ben/.pip/pip.log
```