Update travis.yml

Author: coderius

.travis.yml

@@ -9,14 +9,12 @@ php:
 
 install:
   - composer self-update
-  - composer global require "fxp/composer-asset-plugin:^1.2.0"
+  - composer global require "fxp/composer-asset-plugin:^1.2"
   - composer install
 
 before_script:
   - travis_retry composer self-update
   - travis_retry composer install --no-interaction --prefer-source --dev
-  - rm composer.lock
-  - composer install --no-interaction --prefer-source
 
 script:
   - composer info | sort