build: run `apt upgrade` in appimage script

deployment_scripts/appimage/README.md

@@ -8,7 +8,6 @@ monkey_island AppImage using appimage-builder.
 ## Building an AppImage
 
 1. Create a clean VM or LXC (not docker!) based on Ubuntu 18.04.
-1. Update the OS with `sudo apt update && sudo apt upgrade`
 1. Copy the `deployment_scripts/appimage` directory to `$HOME/` in the VM.
 1. Run `sudo -v`.
 1. On the VM, `cd $HOME/appimage`

deployment_scripts/appimage/build_appimage.sh

@@ -55,6 +55,7 @@ install_nodejs() {
 
 install_build_prereqs() {
     sudo apt update
+    sudo apt upgrade
 
     # appimage-builder prereqs
     sudo apt install -y python3 python3-pip python3-setuptools patchelf desktop-file-utils libgdk-pixbuf2.0-dev fakeroot strace