Fix runnable-textpacker.jar download

Adds 'await' to ensure the download will be complete.

Without this the download might never complete. This issue occurred on a Linux OS (which seem to handle file streams a bit different than some other OSs).
Effects of not fixing this are that the java execution following this download fails for funny "corrupted jar" and other reasons - depending on the size and content of the incomplete jar file.

gulp/image-resources.js

@@ -94,7 +94,7 @@ export async function buildAtlas() {
             const escapedLink = JSON.stringify(runnableTPSource);
 
             try {
-                execute(`curl -o runnable-texturepacker.jar ${escapedLink}`);
+                await execute(`curl -o runnable-texturepacker.jar ${escapedLink}`);
             } catch {
                 throw new Error("Failed to download runnable-texturepacker.jar!");
             }