Update MultiBackend.php

In case you named your driver in camel case (we did), the source (which is now lower case only) will no longer match the key in $this->drivers (which contains the original keys from the file) and the loading of the driver will fail

module/VuFind/src/VuFind/ILS/Driver/MultiBackend.php

@@ -258,8 +258,6 @@ class MultiBackend extends AbstractBase implements ServiceLocatorAwareInterface
      */
     protected function getUninitializedDriver($source)
     {
-        $source = strtolower($source);
-
         // We don't really care if it's initialized here.  If it is, then there's
         // still no added overhead of returning an initialized driver.
         if (isset($this->cache[$source])) {