fix(btm): Expose belongs to many getter similar to other associations (#6551)

lib/associations/belongs-to-many.js

@@ -428,13 +428,10 @@ BelongsToMany.prototype.injectAttributes = function() {
   return this;
 };
 
-BelongsToMany.prototype.injectGetter = function(obj) {
-  var association = this;
-
-  obj[this.accessors.get] = function(options) {
+BelongsToMany.prototype.get = function(instance, options) {
   options = Utils.cloneDeep(options) || {};
 
-    var instance = this
+  var association = this
     , through = association.through
     , scopeWhere
     , throughWhere;
@@ -488,6 +485,13 @@ BelongsToMany.prototype.injectGetter = function(obj) {
   }
 
   return model.findAll(options);
+};
+
+BelongsToMany.prototype.injectGetter = function(obj) {
+  var association = this;
+
+  obj[this.accessors.get] = function(options) {
+    return association.get(this, options);
   };
 
   obj[this.accessors.count] = function(options) {