Update install-toolchain.sh

Author: MaxDesiatov

scripts/install-toolchain.sh

@@ -18,7 +18,7 @@ fi
 
 case $(uname -s) in
   Darwin)
-    toolchain_download="$swift_tag-macos_x86_64.tar.gz"
+    toolchain_download="$swift_tag-macos_x86_64.pkg"
     echo '-macos' >> .swift-version
   ;;
   Linux)