Set forceUpdate flag in refresh method

Closes #2431

Author: marijnh

lib/codemirror.js

@@ -4214,6 +4214,7 @@
     refresh: methodOp(function() {
       var oldHeight = this.display.cachedTextHeight;
       regChange(this);
+      this.curOp.forceUpdate = true;
       clearCaches(this);
       this.scrollTo(this.doc.scrollLeft, this.doc.scrollTop);
       updateGutterSpace(this);