Pull request: scripts: don't use features not guaranteed by posix

Merge in DNS/adguard-home from 2276-fix-portability to master

Updates #2276.

Squashed commit of the following:

commit 3019099f2498923495575873daf372598aa72478
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Dec 31 14:31:02 2020 +0300

    scripts: don't use features not guaranteed by posix

scripts/make/build-release.sh

@@ -349,7 +349,7 @@ echo "{
 			echo "  \"download_${platform}\": \"${version_download_url}/${filename}\"," >> "$version_json"
 		fi
 
-		: "$(( i++ ))"
+		i="$(( i + 1 ))"
 	done
 )