replace 'problems' key with 'exercises' in config.json

[cgrayson]

see #108

[cgrayson]

I forgot to point out that as of exercism/x-api#137, it is safe to remove problems.

[NobbZ]

I'd appreciate if you put the keys for each exercise in the following order:

• slug
• topics
• difficulty

Also I prefer to have the active exercises listed before the inactive ones, so it would be nice if you move exercises at the location that was prviously occupied by the problems key.

After that I think we are ready to merge this one as a base for the re-evaluation done in #107. Thanks for your effort so far.

Please do also add a FIXES-note in your commit-message or PR description.

[cgrayson]

Changes made.

Please do also add a FIXES-note in your commit-message or PR description.

I didn't include a FIXES note previously because this PR only addresses the first of 3 items listed in #108, but without updating difficulty beyond a default of "1" or adding anything in topics. But I can add "fixes…" when I squash these commits, if you want me to.

[NobbZ]

Of course you are right on steps 2 and 3 of #108, I didn't realize them when glancing over the ticket.