mongodb#1930 add required return statements

Author: Treggats

src/Relations/BelongsToMany.php

@@ -171,6 +171,7 @@ public function sync($ids, $detaching = true)
     public function updateExistingPivot($id, array $attributes, $touch = true)
     {
         // Do nothing, we have no pivot table.
+        return $this;
     }
 
     /** @inheritdoc */

src/Schema/Blueprint.php

@@ -274,6 +274,8 @@ public function create($options = [])
     public function drop()
     {
         $this->collection->drop();
+
+        return $this;
     }
 
     /** @inheritdoc */