message: docs(dev-infra): update format commands described in DEVELOPER.md
  This commit updates DEVELOPER.md to describe the latest formatting
  command 'ng-dev' and removed deprecated 'gulp' command.
  Fixes
  PR Close
diff: @@ -96,8 +96,9 @@ Angular uses [clang-format](http://clang.llvm.org/docs/ClangFormat.html) to form
  If the source code is not properly formatted, the CI will fail and the PR cannot be merged.
  You can automatically format your code by running:
  -- `yarn gulp format`: re-format only edited source code.
  -- `yarn gulp format:all`: format _all_ source code
  +- `yarn ng-dev format changed [shaOrRef]`: format only files changed since the provided sha/ref. `shaOrRef` defaults to `master`.
  +- `yarn ng-dev format all`: format _all_ source code
  +- `yarn ng-dev format files <files..>`: format only provided files
  A better way is to set up your IDE to format the changed file on each file save.
  