Merge pull request #2541 from kkimurak/set-bundler-version-based-on-gemfile-lock

Update `bundler` from 2.1.4 to 2.3.6

Author: sachilles

assets/build/install.sh

@@ -90,6 +90,10 @@ fi
 GITLAB_SHELL_VERSION=${GITLAB_SHELL_VERSION:-$(cat ${GITLAB_INSTALL_DIR}/GITLAB_SHELL_VERSION)}
 GITLAB_PAGES_VERSION=${GITLAB_PAGES_VERSION:-$(cat ${GITLAB_INSTALL_DIR}/GITLAB_PAGES_VERSION)}
 
+# install bundler: use version specified in Gemfile.lock
+BUNDLER_VERSION="$(grep "BUNDLED WITH" ${GITLAB_INSTALL_DIR}/Gemfile.lock -A 1 | grep -v "BUNDLED WITH" | tr -d "[:space:]")"
+gem install bundler:"${BUNDLER_VERSION}" 
+
 # download golang
 echo "Downloading Go ${GOLANG_VERSION}..."
 wget -cnv https://storage.googleapis.com/golang/go${GOLANG_VERSION}.linux-amd64.tar.gz -P ${GITLAB_BUILD_DIR}/