Broken in IE10/11

[jhildenbiddle]

Two issues:

docsify-copy-code/index.js

Lines 6 to 8 in 7cbe2d4

	var codeBlocks = document.querySelectorAll("pre[v-pre]");
	codeBlocks.forEach((element, i, obj) => {

1. querySelectorAll returns a NodeList, and not all browsers provide a forEach method on NodeLists.

2. Arrow functions are not support in IE (or older evergreen browsers).

Fixed by #3

[jperasmus]

Hi @jhildenbiddle, thanks for your contributions, it is much appreciated! I originally put this plugin together quickly for a specific use case we had targeting developers specifically on modern browsers. Thanks for your efforts to improve it.