Fix installation command

[koppor]

When I try to install log4brains according to README.md, I get an error:

$ npm install -g @log4brains-cli @log4brains-web
npm ERR! code EINVALIDTAGNAME
npm ERR! Invalid tag name "@log4brains-cli": Tags may not have any characters that encodeURIComponent encodes.

When I use / instead of -, it seems to work.

This is also in line with the command line shown at https://www.npmjs.com/package/@log4brains/cli

[thomvaill]

Well spotted! Thanks