Update fast_gettext requirement from >= 2.1, < 4 to >= 2.1, < 5

Updates the requirements on [fast_gettext](https://github.com/grosser/fast_gettext) to permit the latest version.
- [Changelog](https://github.com/grosser/fast_gettext/blob/master/CHANGELOG)
- [Commits](grosser/fast_gettext@v2.1.0...v2.4.0)

---
updated-dependencies:
- dependency-name: fast_gettext
  dependency-version: 2.4.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

puppet.gemspec

@@ -25,7 +25,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency('concurrent-ruby', '~> 1.0')
   spec.add_runtime_dependency('deep_merge', '~> 1.0')
   spec.add_runtime_dependency('facter', ['>= 4.3.0', '< 5'])
-  spec.add_runtime_dependency('fast_gettext', '>= 2.1', '< 4')
+  spec.add_runtime_dependency('fast_gettext', '>= 2.1', '< 5')
   spec.add_runtime_dependency('getoptlong', '~> 0.2.0')
   spec.add_runtime_dependency('locale', '~> 2.1')
   spec.add_runtime_dependency('multi_json', '~> 1.13')