Updated composer dependencies

composer.json

@@ -23,6 +23,9 @@
     "require": {
         "yiisoft/yii2": ">=2.0.7"
     },
+    "require-dev": {
+        "phpunit/phpunit": "4.8.36"
+    },
     "autoload": {
         "psr-4": {
             "lhs\\Yii2SaveRelationsBehavior\\": "src/"
@@ -31,5 +34,11 @@
     "config": {
         "process-timeout": 1800,
         "preferred-install": "dist"
+    },
+    "repositories": [
+        {
+            "type": "composer",
+            "url": "https://asset-packagist.org"
         }
+    ]
 }