ui: bump regexp_parser in /server/src/main/webapp/WEB-INF/rails

Bumps [regexp_parser](https://github.com/ammar/regexp_parser) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/ammar/regexp_parser/releases)
- [Changelog](https://github.com/ammar/regexp_parser/blob/master/CHANGELOG.md)
- [Commits](ammar/regexp_parser@v2.3.0...v2.3.1)

---
updated-dependencies:
- dependency-name: regexp_parser
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

server/src/main/webapp/WEB-INF/rails/Gemfile.lock

@@ -147,7 +147,7 @@ GEM
     rb-fsevent (0.11.1)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    regexp_parser (2.3.0)
+    regexp_parser (2.3.1)
     rspec (3.11.0)
       rspec-core (~> 3.11.0)
       rspec-expectations (~> 3.11.0)