Makes sure that the property of a style is not an url

I actually got a bug with background-image property
pointing to cloudfront with this url:
  https://d3r0d0kb2vhuxd.cloudfront.net

The viewportUnitExpression regex matched the url
and the url got rewritten.

This is a fix to avoid that.

viewport-units-buggyfill.js

@@ -26,6 +26,8 @@
   var options;
   var userAgent = window.navigator.userAgent;
   var viewportUnitExpression = /([+-]?[0-9.]+)(vh|vw|vmin|vmax)/g;
+  var url = /(https?:)?\/\//
+
   var forEach = [].forEach;
   var dimensions;
   var declarations;
@@ -289,7 +291,7 @@
       }
 
       viewportUnitExpression.lastIndex = 0;
-      if (viewportUnitExpression.test(value)) {
+      if (viewportUnitExpression.test(value) && !url.test(value)) {
         declarations.push([rule, name, value]);
         options.hacks && options.hacks.findDeclarations(declarations, rule, name, value);
       }