make sed command fails on macOS

[jamesstout]

james@Jamess-iMac: ~/Projects/nextcloud/server/apps/maps on master
$ make
...
sed -i 's/L\.Browser\.touch/L.Browser.mobile/g' node_modules/leaflet.elevation/dist/Leaflet.Elevation-0.0.2.min.js
sed: 1: "node_modules/leaflet.el ...": extra characters at the end of n command
make[1]: *** [npm] Error 1
make: *** [build] Error 2

A portable (not POSIX though, sed -i is not POSIX-compliant) fix is:

sed -i.bak 's/L\.Browser\.touch/L.Browser.mobile/g' \
node_modules/leaflet.elevation/dist/Leaflet.Elevation-0.0.2.min.js && rm \
node_modules/leaflet.elevation/dist/Leaflet.Elevation-0.0.2.min.js.bak

[jamesstout]

Submitted a PR: #243 for review.