blast_repo fixes (#75)

* blast_repo fixes

auto-publish

* Update README.md

prep to publish 1.2.1 (#65)

Make the version be 1.2.0. (#59)

We haven't released 1.2.0 yet, so making it 1.2.1 is unnecessary.

Prepare to publish for stable null safety (#45)

Allow the 2.12 dev SDKs (#36)

Also bump deps to the `-nullsafety` versions and remove the dependency
overrides.

Prepare for the 2.11 dev SDKs (#35)

Bump the upper bound to allow 2.10 stable and 2.11.0 dev SDK versions.

update to the 2.10 dev sdk (#31)

* update to the 2.10 dev sdk

* fix sdk version in travis.yml

* depend on 2-10 version of js/meta

allow the <=2.9.10 stable sdk and bump version (#29)

merge null_safety branch into master (#28)

* Migrate package to Null Safety.

- Update CHANGELOG.md.
- Add unsound entry point for test, so it can be run.
- Update SDK dependency to 2.9.0-1
- Updates travis config to run nnbd tests/analysis 
- Adds dependency overrides so tests can be ran in null safety mode
- Updates package version to expected pre-release version
- Updates sdk constraints to restrict to dev sdks with the allow list

Co-authored-by @lrhn.