sync_default_gems.rb: fix links to GitHub issues

- Substitute `GH-xxxx` which does not contain `#` too.
- Split each substitutions.

tool/sync_default_gems.rb

@@ -422,13 +422,16 @@ def message_filter(repo, sha)
   log = STDIN.read
   log.delete!("\r")
   url = "https://github.com/#{repo}"
-  print "[#{repo}] ", log.gsub(/\b(?:(?i:fix(?:e[sd])?) +|GH-)\K#(?=\d+\b)|\(\K#(?=\d+\))/) {
+  log.gsub!(/\b(?:(?i:fix(?:e[sd])?) +)\K#(?=\d+\b)|\bGH-#?(?=\d+\b)|\(\K#(?=\d+\))/) {
     "#{url}/pull/"
-  }.gsub(%r{(?<![-\[\](){}\w@/])(?:(\w+(?:-\w+)*/\w+(?:-\w+)*)@)?(\h{10,40})\b}) {|c|
+  }
+  log.gsub!(%r{(?<![-\[\](){}\w@/])(?:(\w+(?:-\w+)*/\w+(?:-\w+)*)@)?(\h{10,40})\b}) {|c|
     "https://github.com/#{$1 || repo}/commit/#{$2[0,12]}"
-  }.sub(/\s*(?=(?i:\nCo-authored-by:.*)*\Z)/) {
+  }
+  log.sub!(/\s*(?=(?i:\nCo-authored-by:.*)*\Z)/) {
     "\n\n" "#{url}/commit/#{sha[0,10]}\n"
   }
+  print "[#{repo}] ", log
 end
 
 # NOTE: This method is also used by ruby-commit-hook/bin/update-default-gem.sh