Fix internal:add-to-project. (acquia#2394)

Fixes acquia#2214: BLT doctor detect alias files. (acquia#2221) (acqu…

…ia#2365)

* Don't check if Drush alias exists.

* Fix alias logic.

Bump version to 8.9.11.

Updated version to 8.9.10

Updating version to 8.9.9

Requiring drush ^8.1.15. (acquia#2108)

Removing @self default alias. (acquia#2104)

Adding upper version constraint to Drush 9. (acquia#2090)

Fixes acquia#2013: toggleModules uses non-existent drush option --ski…

…p. (acquia#2014)

Making tests:security-updates Drush 9 compatible. (acquia#2024)