ruby.sh: remove linkage cache on upgrade.

This may not be compatible between portable ruby versions and between
portable and system ruby versions.

Fixes #4485.

Library/Homebrew/utils/ruby.sh

@@ -47,7 +47,7 @@ setup-ruby-path() {
         then
           odie "Failed to install vendor Ruby."
         fi
-        rm -rf "$vendor_dir/bundle/ruby"
+        rm -rf "$vendor_dir/bundle/ruby" "$HOMEBREW_CACHE/linkage.db"
         HOMEBREW_RUBY_PATH="$vendor_ruby_path"
       fi
     fi