fix: trigger Zygisk modules service.sh in parallel (#91)

This commit fixes 2 issues:
- service.sh of files were not being executed in parallel, a behavior described in: https://github.com/topjohnwu/Magisk/blob/master/docs/guides.md#boot-scripts . This was fixed by using "&" in the end of the command to execute the module's service.sh, telling the shell to not block.
- Gradle wrapper used in ReZygisk was old, causing failing CIs.

It also updates the NDK version to ensure we'll be operating smoothly.

module/src/service.sh

@@ -15,7 +15,7 @@ if [ "$(which magisk)" ]; then
       if [ -f "$file/service.sh" ]; then
         cd "$file"
         log -p i -t "zygisk-sh" "Manually trigger service.sh for $file"
-        sh "$(realpath ./service.sh)"
+        sh "$(realpath ./service.sh)" &
         cd "$MODDIR"
       fi
     fi