chore: update travis for new builds syntax (#3022)

Author: Foxandxss

scripts/examples-install-preview.sh

@@ -2,12 +2,5 @@
 
 set -ex -o pipefail
 
-PREFIX=2.0.0-
-
-if [ "$PREVIEW_BRANCH" != "master" ]; then
-  PREVIEW_BRANCH=$PREFIX$(git ls-remote https://github.com/angular/angular | grep $LATEST_RELEASE_BRANCH)
-  PREVIEW_BRANCH=${PREVIEW_BRANCH:0:13}
-fi
-
 ./scripts/examples-install.sh
 (cd public/docs/_examples && npm install angular/{core,common,compiler,platform-browser,platform-browser-dynamic,http,forms,router,upgrade}-builds#$PREVIEW_BRANCH --no-optional)