Override probot/stale defaults, if necessary

[kytrinyx]

Per the discussion in exercism/discussions#128 we
will be installing the probot/stale integration on the Exercism organization on
April 10th, 2017.

By default, probot will comment on issues that are older than 60 days, warning
that they are stale. If there is no movement in 7 days, the bot will close the issue.
By default, anything with the labels security or pinned will not be closed by
probot.

If you wish to override these settings, create a .github/stale.yml file as described
in https://github.com/probot/stale#usage, and make sure that it is merged
before April 10th.

If the defaults are fine for this repository, then there is nothing further to do.
You may close this issue.

[kytrinyx]

I made a mistake.

This was not explicitly documented in the README, but probot/stale requires the presence of a .github/stale.yml file.

If you want the default behavior, you need to add an empty .github/stale.yml file to this repo, otherwise the bot will not be active.