Re-apply fix from merge request #15, which was accidentally removed in commit c0f66de.

Author: Eric Koleda

src/Signer.gs

@@ -192,14 +192,12 @@
   * @return {Object}
   */
   OAuth.prototype.deParam = function(string) {
-    var arr = decodeURIComponent(string)
-        .replace(/\+/g, ' ')
-        .split('&');
+    var arr = string.replace(/\+/g, ' ').split('&');
     var data = {};
 
     for(var i = 0; i < arr.length; i++) {
       var item = arr[i].split('=');
-      data[item[0]] = item[1];
+      data[item[0]] = decodeURIComponent(item[1]);
     }
     return data;
   };