Update rdoc requirement from ~> 3.12 to ~> 6.1

Updates the requirements on [rdoc](https://github.com/ruby/rdoc) to permit the latest version.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v3.12...v6.1.2.1)

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

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

Gemfile.lock

@@ -15,10 +15,8 @@ GEM
       thor (~> 0.14.6)
     guard-rspec (0.6.0)
       guard (>= 0.10.0)
-    json (1.6.5)
     rake (0.9.2.2)
-    rdoc (3.12)
-      json (~> 1.4)
+    rdoc (6.1.2.1)
     rspec (2.8.0)
       rspec-core (~> 2.8.0)
       rspec-expectations (~> 2.8.0)
@@ -38,7 +36,7 @@ DEPENDENCIES
   growl
   guard-rspec
   rake (~> 0.9.2.2)
-  rdoc (~> 3.12)
+  rdoc (~> 6.1)
   rspec
   timecop
   xcodebuild-rb!

xcodebuild-rb.gemspec

@@ -24,15 +24,15 @@ Gem::Specification.new do |s|
       s.add_runtime_dependency(%q<state_machine>, ["~> 1.1.2"])
       s.add_development_dependency(%q<rspec>, [">= 0"])
       s.add_development_dependency(%q<rake>, ["~> 0.9.2.2"])
-      s.add_development_dependency(%q<rdoc>, ["~> 3.12"])
+      s.add_development_dependency(%q<rdoc>, "~> 6.1")
       s.add_development_dependency(%q<guard-rspec>, [">= 0"])
       s.add_development_dependency(%q<growl>, [">= 0"])
       s.add_development_dependency(%q<timecop>, [">= 0"])
     else
       s.add_dependency(%q<state_machine>, ["~> 1.1.2"])
       s.add_dependency(%q<rspec>, [">= 0"])
       s.add_dependency(%q<rake>, ["~> 0.9.2.2"])
-      s.add_dependency(%q<rdoc>, ["~> 3.12"])
+      s.add_dependency(%q<rdoc>, "~> 6.1")
       s.add_dependency(%q<guard-rspec>, [">= 0"])
       s.add_dependency(%q<growl>, [">= 0"])
       s.add_dependency(%q<timecop>, [">= 0"])
@@ -41,7 +41,7 @@ Gem::Specification.new do |s|
     s.add_dependency(%q<state_machine>, ["~> 1.1.2"])
     s.add_dependency(%q<rspec>, [">= 0"])
     s.add_dependency(%q<rake>, ["~> 0.9.2.2"])
-    s.add_dependency(%q<rdoc>, ["~> 3.12"])
+    s.add_dependency(%q<rdoc>, "~> 6.1")
     s.add_dependency(%q<guard-rspec>, [">= 0"])
     s.add_dependency(%q<growl>, [">= 0"])
     s.add_dependency(%q<timecop>, [">= 0"])