Fixed up the width of the arrow boarder. Is is a 45° width so must be cos(PI/4)

Author: mattyclarkson

public/js/lib/models/arrow.js

@@ -135,7 +135,7 @@ if (!('CSSArrowPlease' in window)) window.CSSArrowPlease = {};
       if (borderWidth > 0) {
         css = this._arrowCSS(
           this.get('borderColor'),
-          this.get('size') + (borderWidth * 2),
+          this.get('size') + (borderWidth * 1.41421356), // cos(PI/4) * 2
           'before'
         );
       }