Find replacement for inner1d()

[mgeier]

This deprecation warning appears on Travis-CI when using Python 3.7 (using Ubuntu Xenial):

sfs/mono/drivingfunction.py:8
  /home/travis/build/sfstoolbox/sfs-python/sfs/mono/drivingfunction.py:8: DeprecationWarning: numpy.core.umath_tests is an internal NumPy module and should not be imported. It will be removed in a future NumPy release.
    from numpy.core.umath_tests import inner1d  # element-wise inner product

I don't know what's the best replacement for inner1d(), suggestions and PRs are very welcome!

[hagenw]

Here are some suggestions: https://github.com/numpy/numpy/issues/10815

[spors]

One of the benefits of inner1d was parallel processing. This might not be the case for the replacements.