Bump rack-cors from 1.1.0 to 1.1.1 in /backend

Bumps [rack-cors](https://github.com/cyu/rack-cors) from 1.1.0 to 1.1.1.
- [Release notes](https://github.com/cyu/rack-cors/releases)
- [Changelog](https://github.com/cyu/rack-cors/blob/master/CHANGELOG.md)
- [Commits](cyu/rack-cors@v1.1.0...v1.1.1)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

backend/Gemfile.lock

@@ -107,7 +107,7 @@ GEM
     puma (4.3.1)
       nio4r (~> 2.0)
     rack (2.0.8)
-    rack-cors (1.1.0)
+    rack-cors (1.1.1)
       rack (>= 2.0.0)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)