make ruby tests pass

[jameselkins]

• change handler to conform to test expectation
• change bootstrap.rb server address to use AWS_LAMBDA_RUNTIME_API from ENV
• change bootstrap.rb to load lambda handler properly from LAMBDA_TASK_ROOT
• add ruby2.5 and ruby2.7 runtimes
• add install-ruby script
• use rvm to install rubies
• add ruby-version test for ruby2.7 and ruby2.7
• adjust ruby-hello test to use JSON generation

[jameselkins]

hey @styfle - what's the best way to ask for a review / discuss this with you? I'm a little new to contributing so however you'd prefer I format my pull request, I'd be happy to do so.

Additionally, I noticed that this is probably not going to work correctly end-to-end unless:

1. https://github.com/zeit/now/blob/master/packages/now-cli/src/util/dev/builder.ts#L362 is cast as a RuntimeLiteral (or something else needs to happen? Right now it complains about that when I try to build, I've changed that line to Runtime: asset.runtime as RuntimeLiteral locally)
2. https://github.com/zeit/now/blob/master/packages/now-ruby/install-ruby.ts#L53-L61 is modified to look for the correct gemHome if meta.isDev === true
3. https://github.com/zeit/now/blob/master/packages/now-ruby/install-ruby.ts#L21-L24 needs to be removed of course :)

Please let me know your thoughts on the code!

[jameselkins]

Ah, I see now about https://github.com/zeit/now/pull/3667 - Would make sense to modify that PR a bit more to take my suggestions above into account?

[jameselkins]

hey @styfle - thanks for the suggestions! I made the updates you recommended :)