Fix the browser tests

lib/less/environments/browser.js

@@ -46,6 +46,9 @@ return {
     },
     getCleanCSS: function () {
     },
+    supportsDataURI: function() {
+        return false;
+    },
     pathDiff: function pathDiff(url, baseUrl) {
         // diff between two paths to create a relative path