Forcing composer to self-update in builds

.travis.yml

@@ -23,6 +23,7 @@ before_script:
   - sh -c "if [ '$DB' = 'pgsql' ]; then sudo service postgresql stop; sudo service postgresql start $POSTGRESQL_VERSION; fi"
   - sh -c "if [ '$DB' = 'mysql' ]; then mysql -e 'create database IF NOT EXISTS doctrine_tests_tmp;create database IF NOT EXISTS doctrine_tests;'; fi"
   - sh -c "if [ '$DB' = 'mysqli' ]; then mysql -e 'create database IF NOT EXISTS doctrine_tests_tmp;create database IF NOT EXISTS doctrine_tests;'; fi"
+  - composer self-update
   - composer --prefer-source --dev install
 
 script: phpunit --configuration tests/travis/$DB.travis.xml