Bump strong_migrations from 0.7.2 to 0.7.3

Bumps [strong_migrations](https://github.com/ankane/strong_migrations) from 0.7.2 to 0.7.3.
- [Release notes](https://github.com/ankane/strong_migrations/releases)
- [Changelog](https://github.com/ankane/strong_migrations/blob/master/CHANGELOG.md)
- [Commits](ankane/strong_migrations@v0.7.2...v0.7.3)

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -443,7 +443,7 @@ GEM
       actionpack (>= 4.0)
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
-    strong_migrations (0.7.2)
+    strong_migrations (0.7.3)
       activerecord (>= 5)
     sync (0.5.0)
     term-ansicolor (1.7.1)