Add fix for contenteditable in safari

[damwhit]

Fixes #343

Hello! Thanks for putting together this great library! Here is a small PR to fix the contenteditable bug in safari.

Behavior before (when I took out the safari guard clause)

Behavior with fix

[damwhit]

@yuku I couldn't add you as a reviewer so thought I'd ping you here. Thanks!

[yuku]

v0.1.12 was released

[damwhit]

Thanks for the quick merge and release!