updateOrCreate assumes numeric primary key(s)

I removed the check to see if a property is an ID field while building the
values clause to allow it to work if primary key(s) are strings.

lib/mysql.js

@@ -213,11 +213,7 @@ MySQL.prototype.updateOrCreate = function (model, data, callback) {
     if (props[key] || mysql.id(model, key)) {
       var k = mysql.columnEscaped(model, key);
       var v;
-      if (!mysql.id(model, key)) {
-        v = mysql.toDatabase(props[key], data[key]);
-      } else {
-        v = data[key];
-      }
+      v = mysql.toDatabase(props[key], data[key]);
       if (v !== undefined) {
         fieldsNames.push(k);
         fieldValues.push(v);