Fix Darwin sha256 sum

Author: fcharlie

script/build.sh

@@ -69,5 +69,14 @@ GO111MODULE=on go get github.com/balibuild/bali/cmd/bali
 echo -e "build TunnelSSH \\x1b[32m${TOPLEVEL}\\x1b[0m"
 cd "$TOPLEVEL"
 bali -z
-sha256sum *.tar.gz
+
+SHACMD='sha256sum'
+
+case "$(uname -s)" in
+    *Darwin*)
+        SHACMD='shasum -a 256'
+esac
+
+
+$SHACMD *.tar.gz
 echo -e "\\x1b[32mbuild TunnelSSH success\\x1b[0m"