fix for Matplotlib-2.1.0rc1 (#1842)
fix for Matplotlib-2.1.0rc1 (#1842)

AnchoredText unused import was remove from mpl_toolkit. fix https://github.com/ioam/holoviews/issues/1840
ioam/holoviews,basnijholt/holoviews,basnijholt/holoviews,basnijholt/holoviews,ioam/holoviews,ioam/holoviews