Fix capybara pins for older rubies

Author: Sam Phippen

example_app_generator/generate_app.rb

@@ -48,6 +48,9 @@
     else
       gsub_file "Gemfile", /.*chromedriver-helper.*/, "gem 'webdrivers'"
     end
+    if RUBY_VERSION < "2.4"
+      gsub_file "Gemfile", /.*capybara.*/, "gem 'capybara', '~> 3.10.0'"
+    end
   end
 
   if Rails::VERSION::STRING >= '5.2.0' && Rails::VERSION::STRING < '6'