Move vendor/_rfs.scss (#1)

Reviewed-on: #1
Co-authored-by: Stefan <git@stefn.co.uk>
Co-committed-by: Stefan <git@stefn.co.uk>

.gitignore

@@ -11,3 +11,4 @@ Gemfile.lock
 .env
 .aider*
 resized
+result

_sass/bootstrap/_mixins.scss

@@ -3,7 +3,7 @@
 // Used in conjunction with global variables to enable certain theme features.
 
 // Vendor
-@import "vendor/rfs";
+@import "rfs";
 
 // Deprecate
 @import "mixins/deprecate";