refactor: remove unused import clauses
refactor(ngRepeat): simplify the code

This re-introduce the PR #1018: "refactor(ng-repeat): refactor fix for
#1015" which had been reverted.
chore(travis): make docs generate on the travis leader

The leader tries to push the API docs to docs.angulardart.org, and as
such needs to have the docs built.
Revert "refactor: remove unused import clauses"

This reverts commit 7c2846e34b8a9ed119ed05a4702cb02f8c97dd6c.