Log Message:
py-numexpr: updated to 2.6.8

Changes from 2.6.7 to 2.6.8
---------------------------
- Add check to make sure that f_locals is not actually f_globals when we
  do the f_locals clear to avoid the 310 memory leak issue.
- Compare NumPy versions using distutils.version.LooseVersion to avoid issue
  312 when working with NumPy development versions.
- As part of multibuild, wheels for Python 3.7 for Linux and MacOSX are now
  available on PyPI