Avoid rails app generation error when using last Thor

The last Thor version break `rails generate controller` command.

Related:
- rails/rails#37978

Author: benoittgt

example_app_generator/generate_app.rb

@@ -33,6 +33,10 @@
     append_to_file('Gemfile', "gem 'rails-controller-testing'\n")
   end
 
+  if Rails::VERSION::STRING ~= /^4\./
+    append_to_file('Gemfile', "gem 'thor', '< 1.0'\n")
+  end
+
   if Rails::VERSION::STRING >= '6'
     gsub_file "Gemfile", /.*gem..sqlite3.*/, "gem 'sqlite3', '~> 1.4'"
     gsub_file "Gemfile", /.*rails-controller-testing.*/, "gem 'rails-controller-testing', git: 'https://github.com/rails/rails-controller-testing'"