Added missing postgres user to the travis config.

.travis.yml

@@ -11,6 +11,6 @@ env:
 
 before_script:
   - sh -c "if [ '$DB' = 'mysql' ]; then mysql -e 'create database IF NOT EXISTS yiitest;'; fi"
-  - sh -c "if [ '$DB' = 'postgres' ]; then psql -c 'drop database if exists yiitest;'; fi"
-  - sh -c "if [ '$DB' = 'postgres' ]; then psql -c 'create database yiitest;'; fi"
+  - sh -c "if [ '$DB' = 'postgres' ]; then psql -U postgres -c 'drop database if exists yiitest;'; fi"
+  - sh -c "if [ '$DB' = 'postgres' ]; then psql -U postgres -c 'create database yiitest;'; fi"
 script: phpunit