[test fix] update asset plugin version

Author: lichunqiang

.travis.yml

@@ -19,7 +19,7 @@ cache:
 
 # script run before anything
 before_script:
-    - composer global require "fxp/composer-asset-plugin:1.0.0"
+    - composer global require "fxp/composer-asset-plugin:~1.1.1"
     - composer install
     - cp phpunit.xml.dist phpunit.xml