Perform the where(...).first to find_by(...) refactoring.

This refactoring was automated using the command: bundle exec "ruby refactorings/where_dot_first_to_find_by/app.rb"

lib/auth/github_authenticator.rb

@@ -19,7 +19,7 @@ class Auth::GithubAuthenticator < Auth::Authenticator
       github_screen_name: screen_name,
     }
 
-    user_info = GithubUserInfo.where(github_user_id: github_user_id).first
+    user_info = GithubUserInfo.find_by(github_user_id: github_user_id)
 
     if user_info
       user = user_info.user