relation: add `scope._target` for `hasOne`

Add `_target` property to the scope method created by `hasOne`
relationship. The `_target` property is used by loopback-sdk-angular.

lib/relation-definition.js

@@ -1055,6 +1055,7 @@ RelationDefinition.hasOne = function (modelFrom, modelTo, params) {
       var relationMethod = relation.related.bind(relation)
       relationMethod.create = relation.create.bind(relation);
       relationMethod.build = relation.build.bind(relation);
+      relationMethod._targetClass = relationDef.modelTo.modelName;
       return relationMethod;
     }
   });

test/relations.test.js

@@ -658,6 +658,9 @@ describe('relations', function () {
       });
     });
 
+    it('should set targetClass on scope property', function() {
+      should.equal(Supplier.prototype.account._targetClass, 'Account');
+    });
   });
 
   describe('hasAndBelongsToMany', function () {