Work around brew update failing

Author: nurupo

.travis/script.sh

@@ -59,8 +59,10 @@ elif [ "$TARGET" = "Windows" ]; then
   mkdir artifacts
   cp -a build/*.zip artifacts
 elif [ "$TARGET" = "macOS" ]; then
-  # updating fails sometimes, unable to fetch data off homebrew GitHub repo, so retry a few times
-  brew update || brew update || brew update || brew update || brew update
+  # updating fails sometimes, unable to fetch data off homebrew GitHub repo, so keep retrying
+  until brew update; do
+    sleep 30
+  done
   brew install p7zip
   mkdir -p tmp/tmp
   cd tmp/tmp