[travis-ci] Enable cache

Composer is updated for to prevent cache invalidation due stat operations over cached files

Author: Maks3w

.travis.yml

@@ -2,6 +2,10 @@ sudo: false
 
 language: php
 
+cache:
+  directories:
+    - $HOME/.composer/cache
+
 matrix:
   fast_finish: true
   include:
@@ -22,6 +26,7 @@ notifications:
 
 before_install:
   - if [[ $EXECUTE_COVERAGE != 'true' ]]; then phpenv config-rm xdebug.ini || return 0 ; fi
+  - composer self-update
 
 install:
   - composer install