Blender Git Loki

Fix Squash and Stretch naming in the Pose Brush deform mode

Previusly it was using the / character, which implies that there is one
deformation mode and and invert deformation mode like in the other two
deformation, but squash and stretch is only one deformation mode and
does not have an invert mode.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8463