(#5) Enabled xvfb on Linux

Author: s1hofmann

.build/run_linux.sh

@@ -9,5 +9,5 @@ npm run compile
 echo "init e2e test subpackage"
 npm --prefix e2e/tests ci
 echo "npm run coverage"
-E2E_TEST=1 npm run coverage
+npm run coverage
 docker exec nut-ci bash -c "bash $PWD/.build/build.sh ${PWD} ${TRAVIS_NODE_VERSION}"

.travis.yml

@@ -26,6 +26,7 @@ addons:
 
 services:
   - docker
+  - xvfb
 
 install:
   - "bash ./.build/setup_${TRAVIS_OS_NAME}.sh"