Please print '****' when a Github token is input

[mato]

When no Github token is configured, we get:

/home/mato/.config/dune/github.token does not exist!

To create a new token, please visit:

   https://github.com/settings/tokens/new

And create a token with a nice name and and the public_repo scope only.

Copy the token
here: [?] Create release v0.6.4 on [email protected]:mirage/mirage-solo5.git? [Y/n]

I.e. in the above I pasted an existing token into the terminal, and got no feedback that it had been input.

I suggest printing a '*' for each character input.

[NathanReb]

That'd be good instead! Thanks for reporting it!