AutoPrefix: remove trailing "\" if present

src/CliProgram/AutoPrefix/AutoPrefixNamespaceManager.php

@@ -48,6 +48,10 @@ class AutoPrefixNamespaceManager implements IAutoPrefixManager {
         if (mb_substr($namespace, 0, 1) !== '\\') {
             $namespace = '\\' . $namespace;
         }
+        if (mb_substr($namespace, -1) === '\\') {
+            $namespace = mb_substr($namespace, 0, -1);
+        }
+
         $this->namespace = $namespace;
         return $this;
     }