IE11 + zoom-image plugin: Exception thrown and not caught

[jhildenbiddle]

Including this plugin throws an "Exception thrown and not caught" error in IE11, preventing further JavaScript execution.

IE11 console references this line:

• lib/docsify.js

[jhildenbiddle]

Apologies. This is an issue with medium-zoom, not docsify.

• Throws error in IE 11 (Windows 10) francoischalifour/medium-zoom#34