Change access specifier on $operators property to match Laravel base query builder class (#1086)

Fixes #1077

src/Jenssegers/Mongodb/Query/Builder.php

@@ -60,7 +60,7 @@ class Builder extends BaseBuilder
      *
      * @var array
      */
-    protected $operators = [
+    public $operators = [
         '=', '<', '>', '<=', '>=', '<>', '!=',
         'like', 'not like', 'between', 'ilike',
         '&', '|', '^', '<<', '>>',