chore: update middleman-sprockets requirement from = 4.0.0 to = 4.1.1

Updates the requirements on [middleman-sprockets](https://github.com/middleman/middleman-sprockets) to permit the latest version.
- [Changelog](https://github.com/middleman/middleman-sprockets/blob/master/CHANGELOG.md)
- [Commits](middleman/middleman-sprockets@v4.0.0...v4.1.1)

---
updated-dependencies:
- dependency-name: middleman-sprockets
  dependency-version: 4.1.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

govuk_tech_docs.gemspec

@@ -52,7 +52,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "middleman-livereload"
   spec.add_dependency "middleman-search-gds"
   # middleman-sprockets is very old and out of date.  V4.1.0 has a breaking change.  Will look to replace with gem "dartsass-sprockets" or uses sass in the package.json
-  spec.add_dependency "middleman-sprockets", "4.0.0"
+  spec.add_dependency "middleman-sprockets", "4.1.1"
   spec.add_dependency "middleman-syntax"
   spec.add_dependency "mutex_m" # TODO: remove once activesupport declares this itself.
   spec.add_dependency "nokogiri"