Fix capybara pins for older rubies

Author: Sam Phippen

Gemfile-rails-dependencies

@@ -35,4 +35,3 @@ else
   end
   gem 'activerecord-jdbcsqlite3-adapter', platforms: [:jruby]
 end
-

example_app_generator/generate_app.rb

@@ -40,6 +40,9 @@
   end
 
   if Rails::VERSION::STRING >= "5.1.0"
+    if RUBY_VERSION < "2.4"
+      gsub_file "Gemfile", /.*capybara.*/, "gem 'capybara', '~> 3.10.0'"
+    end
     gsub_file "Gemfile", /.*selenium-webdriver.*/, "gem 'selenium-webdriver', '<= 3.14'"
   end