Migrate to null safety (dart-lang/pub_semver#52)

- Switch to a major version bump.
- Reformat `.travis.yml`. Indent list elements to the same position as
  the containing key. This matches yaml style in other Google files.
- Update SDK constraints to use the `2.11.0` dev SDKs.
- Renames some variables with noise word "the" to match the field name
  and avoid the shadowing with `this.`.
- Add override for analyzer package.

Co-authored-by: Nate Bosch <nbosch1@gmail.com>
10 files changed
tree: 26c1a80eea99e931a91711874e02c0542652e8f3
  1. pkgs/