[flutter] Make WASM recompilation mandatory before publishing.

spine-flutter/compile-wasm.sh

@@ -1,4 +1,5 @@
 #!/bin/sh
+set -e
 dir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null && pwd )"
 pushd $dir > /dev/null
 mkdir -p lib/assets/