get_releases.py should default to more than 30 days

[chriscool]

There can be more than 30 days between 2 Git Rev News editions, so 30 days may make us miss some releases.

It's better to get releases that we already talked about rather than miss releases, so I suggest a 40 or 45 days default rather than 30.

This is a follow up from #3.

@gaalcaras

[chriscool]

Also we often prepare the releases on Saturday or Sunday, and we publish the next Wednesday, so there is already a potential window for missing releases.

[gaalcaras]

Okay, I'll change the default settings.

we publish the next Wednesday, so there is already a potential window for missing releases.

Once the script gets more reliable, maybe a solution would be to generate the releases section when RevNews is published? Could also tie in with git/git.github.io#273

[gaalcaras]

Another thing we could do is being clear about the period in which the releases occured. Maybe something like:

# Releases

The following releases were issued between 2018-04-01 and 2018-05-01:

+ ...