ci(travis): restore before_install

.travis.yml

@@ -1,7 +1,8 @@
 if: tag IS present
+language: python
 services:
   - docker
-install:
+before_install:
   - |
     if [ ! -z "$encrypted_103700d0e85f_key" ]; then
       openssl aes-256-cbc -K $encrypted_103700d0e85f_key -iv $encrypted_103700d0e85f_iv -in scripts/launchpad-secret.key.enc -out scripts/launchpad-secret.key -d
@@ -11,6 +12,9 @@ install:
     fi
   - source ./scripts/common.sh
   - docker pull $BUILD_IMAGE
+install:
+  # this is to skip default "pip install -r requirements.txt" on travis
+  - true
 before_deploy:
   - pip3 install -r requirements.txt # docker image has outdated pip versions
   - ./ul build-release $TRAVIS_TAG