Fix an exception when pressing 'h' in newer numpy versions
Fix an exception when pressing 'h' in newer numpy versions

Casting behaviour has changed in newer numpy versions.
This fix makes some code in the help-text compatible with the newer
numpy

arikpoz/deep-visualization-toolbox,arikpoz/deep-visualization-toolbox,yosinski/deep-visualization-toolbox,arikpoz/deep-visualization-toolbox,yosinski/deep-visualization-toolbox