Pin pypy2.7 version in Travis
Pin pypy2.7 version in Travis

There is some issue with pypy2.7-5.8.0 in Travis. This probably does not
solve the *root* issue, but updating the pypy version does seem to fix
the build, so in the interest of unblocking the project, we will merge
this change.

pypa/setuptools,pypa/setuptools,pypa/setuptools