sed in generate.sh throws error

in the [generate.sh](https://github.com/CIRCL/potiron/blob/master/bin/generate.sh#L10) script, the command `sed -e "s_##LOGO##_${logo}_g"` throws the error ``sed: -e expression #1, char 22: unknown option to `s' ``. i changed it to `sed -e "s%##LOGO##%${logo}%g"` which worked for me.