[Travis] Switch to trusty enviroment

.travis.yml

@@ -1,4 +1,5 @@
-sudo: false
+sudo: required
+dist: trusty
 language: php
 
 # run tests on php misc php versions
@@ -15,8 +16,6 @@ branches:
 
 # setup requirements for running unit tests
 before_script:
-  # Get latests version of composer which is faster (and to attempt to avoid memory issues with legacy package)
-  - travis_retry composer self-update
   # Disable xdebug to speed things up as we don't currently generate coverge on travis
   - if [ $TRAVIS_PHP_VERSION != "hhvm" ]; then phpenv config-rm xdebug.ini ; fi
   # Avoid issues on composer install since we pull in both legacy and platform stack