Fix Gems search to handle updated Rubygems.org

Rubygems.org went through a redesign lately, and broke this portion of the workflow.

Notable bits:

* Use the Rubygems.org API, instead of parsing HTML search results
* Use HTTPS, as per Rubygems.org docs
* Simplify `Repo::check`
    * Don’t need multiple `return true` conditionals

The version number has been bumped to v2.01 to reflect this as a patch-level change, and the workflow & various JSON files (in & out of the workflow) have been updated.

Resolves #40