fix https://github.com/orthes/medium-editor-insert-plugin/issues/39
support Mac OS X cmd key
Merge branch 'fix-select-all-chrome' of https://github.com/OmniaGM/medium-editor-insert-plugin into OmniaGM-fix-select-all-chrome

Conflicts:
	dist/js/addons/medium-editor-insert-plugin.js
	dist/js/addons/medium-editor-insert-plugin.min.js
	dist/js/medium-editor-insert-plugin.all.min.js
	src/js/medium-editor-insert-plugin.js