Update .travis.yml

Author: matthieudolci

.travis.yml

@@ -18,11 +18,11 @@ jobs:
     - stage: build docker latest
       script: 
         - make build-docker
-        - docker login -u $DOCKER_USER -p '$DOCKER_PASS'
+        - docker login -u $DOCKER_USER -p $DOCKER_PASS
         - make push
     - stage: build docker tag
       script: 
         - TAG=$TRAVIS_TAG make build-docker
-        - docker login -u $DOCKER_USER -p '$DOCKER_PASS'
+        - docker login -u $DOCKER_USER -p $DOCKER_PASS
         - TAG=$TRAVIS_TAG make push