Use set -e so build fails if any command fail

Author: aarranz

.travis.yml

@@ -20,6 +20,7 @@ before_script:
     - sed -i 's/latest-composable/${VERSION}/' docker-compose.yml
 
 script:
+    - set -e
     - docker build -t fiware/wirecloud:${VERSION} .
     - docker-compose up -d
     - sleep 40