Minor fixes and tweaks

[gianick]

1. Bumped sbt from 1.9.6 to 1.9.7
2. Updated the latest version in the README file and made some other small improvements. Instead of using an unordered list, I thought using a numbered one would make it more obvious that the steps should be followed in that order.
3. Added a closing message with a link to the "Compiler Options Lookup Table" in the ScalacOptionsMigration file, fixed a minor typo and made some messages more consistent.
4. Fixed some linting warnings.
5. Minor fix to the CONTRIBUTING.md file. The bin/scalafmt --diff command formats files listed in git diff against the master branch but since it does not exist, it was causing an exception.