Gracefully handle rate limit related errors (#810)

Fixes #458

app/controllers/application_controller.rb

@@ -15,6 +15,9 @@ class ApplicationController < ActionController::Base
   rescue_from Octokit::BadGateway, Octokit::ServiceUnavailable, Octokit::InternalServerError, Octokit::ServerError do |exception|
     handle_exception(exception, :service_unavailable, I18n.t("exceptions.octokit.unavailable"))
   end
+  rescue_from Octokit::AbuseDetected, Octokit::TooManyRequests do |exception|
+    handle_exception(exception, :service_unavailable, I18n.t("exceptions.octokit.rate_limit"))
+  end
   rescue_from Faraday::ClientError do |exception|
     handle_exception(exception, :service_unavailable, I18n.t("exceptions.faraday.connection_failed"))
   end

config/locales/en.yml

@@ -28,5 +28,6 @@ en:
     octokit:
       unauthorized: 'Your GitHub token seems to be invalid'
       unavailable: 'Having issues connecting to GitHub'
+      rate_limit: 'GitHub rate limit exceeded, try again in a few minutes'
     faraday:
       connection_failed: 'You seem to be offline'