Fix docker login credentials

.gitlab-ci.yml

@@ -32,7 +32,7 @@ build_image:
     - ''
   script:
     - docker build -t clarinpl/speller2 .
-    - echo $DOCKER_PASSWORD
+    - echo $DOCKER_PASSWORD > pass.txt
     - cat pass.txt | docker login --username $DOCKER_USERNAME --password-stdin
     - rm pass.txt
     - docker push clarinpl/speller2