Updated build

Author: Simon Hofmann

.travis.yml

@@ -35,7 +35,6 @@ env:
 
 before_install:
   - chmod +x ./ci/$BUILD_TASK/$BUILD_TASK.sh
-  - npm i -g prebuild
 
 install: travis_wait 30 docker pull justadudewhohacks/opencv4nodejs-ci:$TAG
 
@@ -46,6 +45,7 @@ script:
 
 after_success:
   - if [[ $TRAVIS_TAG != "" ]]; then
+    npm install;
     npm run prebuild -- -u $GITHUB_TOKEN;
     fi
   - if [ $BUILD_TASK = 'cover' ]; then