Different way of setting the npm version

src/freedombone-image-customise

             exit 8793636
         fi
         chroot "$rootdir" chmod +x /root/npm_install.sh
-        chroot "$rootdir" npm_install=$NPM_VERSION /root/npm_install.sh
+        sed -i "s|t=\"\${npm_install}\"|t=\"$NPM_VERSION\"|g" $rootdir/root/npm_install.sh
+        chroot "$rootdir" /root/npm_install.sh
     fi
 
     git clone https://github.com/ssbc/patchwork $rootdir/etc/patchwork