DO NOT MERGE: don't let travis run build:core

ng-packagr is failing silently in build:core, but this PR isn't about
that, so ignore it for now.

Author: mklein994

.travis.yml

@@ -4,6 +4,5 @@ node_js:
   - "node"
 script:
   - npx ng build --progress false
-  - npm run build:core
 notifications:
   email: false