zim-filter/install-zim-tools.sh: apt packages 'docopt-dev' & 'ninja' don't exist on Ubuntu 20.04

[holta]

@georgejhunt

Can you remove or rename these 2 packages do not exist on Ubuntu 20.04 ?
https://github.com/iiab/iiab-factory/blob/master/content/kiwix/zim-filter/install-zim-tools.sh#L20-L21

# apt install ninja docopt-dev
...
E: Unable to locate package ninja
E: Unable to locate package docopt-dev

Just FYI similar packages are installed automatically, so commenting out of both above lines is possibly best?

# apt list ninja-build libdocopt-dev
Listing... Done
libdocopt-dev/focal,now 0.6.2-2build1 amd64 [installed]
ninja-build/focal,now 1.10.0-1build1 amd64 [installed,automatic]

cc: @deldesir @curtathompson