update tests configuration

Author: igor-chepurnoi

.travis.yml

@@ -10,14 +10,12 @@ sudo: false
 cache:
   directories:
     - $HOME/.composer/cache
-    - vendor
 
 install:
   - travis_retry composer self-update && composer --version
-  - travis_retry composer global require "fxp/composer-asset-plugin:~1.1.1"
   - export PATH="$HOME/.composer/vendor/bin:$PATH"
   - travis_retry composer install --prefer-dist --no-interaction
 
 script:
   - vendor/friendsofphp/php-cs-fixer/php-cs-fixer fix --dry-run --diff
-  - phpunit --verbose $PHPUNIT_FLAGS
+  - phpunit --verbose

composer.json

@@ -28,5 +28,11 @@
         "psr-4": {
             "yii2mod\\cashier\\": ""
         }
-    }
+    },
+    "repositories": [
+        {
+            "type": "composer",
+            "url": "https://asset-packagist.org"
+        }
+    ]
 }