Fixed Travis failure: moved matplotlib import to plot_xs instead of at the module level
Fixed Travis failure: moved matplotlib import to plot_xs instead of at the module level

paulromano/openmc,mit-crpg/openmc,liangjg/openmc,walshjon/openmc,smharper/openmc,mit-crpg/openmc,walshjon/openmc,smharper/openmc,johnnyliu27/openmc,liangjg/openmc,shikhar413/openmc,walshjon/openmc,liangjg/openmc,wbinventor/openmc,amandalund/openmc,liangjg/openmc,smharper/openmc,johnnyliu27/openmc,johnnyliu27/openmc,wbinventor/openmc,paulromano/openmc,shikhar413/openmc,paulromano/openmc,amandalund/openmc,shikhar413/openmc,mit-crpg/openmc,walshjon/openmc,wbinventor/openmc,amandalund/openmc,mit-crpg/openmc,paulromano/openmc,wbinventor/openmc,bhermanmit/openmc,amandalund/openmc,smharper/openmc,shikhar413/openmc,bhermanmit/openmc,johnnyliu27/openmc