Build meteor app in custom GitLab hook

How do I build a meteor app (do 'meteor build .') in a GitLab custom hook? The custom hook is run by the user git who does not seem to have any possibility to run meteor build.

Therefore I want to change the user in the script to someone who is known to be able to build the app.

This is my bash file until now:

#!/bin/sh
#

# The deployed directory
DEPLOYDIR=/var/www/site/

echo " - Starting checkout"
GIT_WORK_TREE="$DEPLOYDIR" git checkout -f
echo " - Finished checkout" 

echo " - Starting meteor build"
#not working yet
sudo su - nodejs
cd "$DEPLOYDIR"
meteor build .