Make parser.js compatible with showdown >= 1.3.0

Parser reassigns showdown's makeHtml and leaves "this" reference hanging. This binds the converter object to makeHtml method fixing the issue.

Author: tivie

src/js/parser.js

@@ -8,7 +8,7 @@ var Parser = function(config) {
         this.parseMdown = config.parsingFunction;
     } else {
         var converter = new showdown.Converter();
-        this.parseMdown = converter.makeHtml;
+        this.parseMdown = converter.makeHtml.bind(converter);
     }
 }
 
@@ -120,4 +120,4 @@ Parser.prototype.getTitle = function(mdown){
     return match? match[1].trim() : '';
 }
 
-module.exports = Parser;
+module.exports = Parser;