Change the way `marked` is imported to keep IE11 support

[tjrobinson]

marked 0.7.0 has a breaking change for IE11: markedjs/marked#1585

I believe the fix for angular-marked, if it's being used with marked 0.7.0, is to change this line:

angular-marked/lib/angular-marked.js

Line 191 in c10be54

m = require('marked');

To: m = require('marked/lib/marked')