Bump stringio from 3.0.9 to 3.1.0

Bumps [stringio](https://github.com/ruby/stringio) from 3.0.9 to 3.1.0.
- [Release notes](https://github.com/ruby/stringio/releases)
- [Changelog](https://github.com/ruby/stringio/blob/master/NEWS.md)
- [Commits](ruby/stringio@v3.0.9...v3.1.0)

---
updated-dependencies:
- dependency-name: stringio
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -300,7 +300,7 @@ GEM
       actionpack (>= 5.2)
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
-    stringio (3.0.9)
+    stringio (3.1.0)
     thor (1.3.0)
     tilt (2.3.0)
     timeout (0.4.1)