Updated matplotlib version in .travis.yml
Updated matplotlib version in .travis.yml

ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews,vascotenner/holoviews,vascotenner/holoviews,mjabri/holoviews,ioam/holoviews,mjabri/holoviews,basnijholt/holoviews,ioam/holoviews,mjabri/holoviews,basnijholt/holoviews