From 5c83729be96a852927fe7c44cd089ce243f01c7f Mon Sep 17 00:00:00 2001
From: kiendang <kiend@pm.me>
Date: Fri, 26 Apr 2019 23:03:40 +0800
Subject: [PATCH] Fix mutable string syntax

---
 Library/Homebrew/utils/github.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Library/Homebrew/utils/github.rb b/Library/Homebrew/utils/github.rb
index e893400da8..9b241f870b 100644
--- a/Library/Homebrew/utils/github.rb
+++ b/Library/Homebrew/utils/github.rb
@@ -47,7 +47,7 @@ module GitHub
   class AuthenticationFailedError < Error
     def initialize(github_message)
       @github_message = github_message
-      message += "GitHub #{github_message}:"
+      message = +"GitHub #{github_message}:"
       if ENV["HOMEBREW_GITHUB_API_TOKEN"]
         message << <<~EOS
           HOMEBREW_GITHUB_API_TOKEN may be invalid or expired; check: