Quiets the docker build to reduce log noise

.travis.yml

@@ -25,7 +25,7 @@ jobs:
       script: make -o docs/lint lint
     - stage: test
       name: Run Makefile unit tests
-      install: docker build --build-arg GITHUB_ACCESS_TOKEN=$GITHUB_ACCESS_TOKEN -t "$IMAGE_NAME" -f Dockerfile .
+      install: docker build --quiet --build-arg GITHUB_ACCESS_TOKEN=$GITHUB_ACCESS_TOKEN -t "$IMAGE_NAME" -f Dockerfile .
       script: docker run "$IMAGE_NAME" bats/test
     - stage: deploy
       name: Deploy to GitHub Releases