Update gc_ruboconfig requirement from ~> 2.26.0 to ~> 2.29.0

Updates the requirements on [gc_ruboconfig](https://github.com/gocardless/ruboconfig) to permit the latest version.
- [Release notes](https://github.com/gocardless/ruboconfig/releases)
- [Changelog](https://github.com/gocardless/gc_ruboconfig/blob/master/CHANGELOG.md)
- [Commits](gocardless/gc_ruboconfig@v2.26.0...v2.29.0)

---
updated-dependencies:
- dependency-name: gc_ruboconfig
  dependency-type: direct:development
...

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

ibandit.gemspec

@@ -3,7 +3,7 @@
 require File.expand_path("lib/ibandit/version", __dir__)
 
 Gem::Specification.new do |gem|
-  gem.add_development_dependency "gc_ruboconfig",   "~> 2.26.0"
+  gem.add_development_dependency "gc_ruboconfig",   "~> 2.29.0"
   gem.add_development_dependency "nokogiri",        "~> 1.6"
   gem.add_development_dependency "pry",             "~> 0.13"
   gem.add_development_dependency "pry-byebug",      "~> 3.9"