Add grammar to 2.2 as well, fixes #729

src/Jenssegers/Mongodb/Query/Builder.php

@@ -85,6 +85,7 @@ class Builder extends BaseBuilder
      */
     public function __construct(Connection $connection, Processor $processor)
     {
+        $this->grammar = new Grammar;
         $this->connection = $connection;
         $this->processor = $processor;
     }

src/Jenssegers/Mongodb/Query/Grammar.php

+<?php namespace Jenssegers\Mongodb\Query;
+
+use Illuminate\Database\Query\Grammars\Grammar as BaseGrammar;
+
+class Grammar extends BaseGrammar
+{
+}