Consider whether to remove empty parens in Ruby snippets

Currently we use empty parens in Ruby snippets in the docs, a'la:

r.table('foo').max()

It seems to be common style in Ruby to elide empty parens like:

r.table('foo').max

ping @mlucy @mglukhovsky @gchpaco. If eliding the empty parens is pretty universal in Ruby code, I think we should do it. But if it's a "some people do, some people don't" then it's not worth bothering since most Ruby devs will be used to seeing empty parens regularly and it won't look off to them.

Note I'm just talking about eliding empty parens, not all parens in Ruby snippets.

Search the documentation for Ruby snippets that use empty parentheses and review the issue's style question against common Ruby conventions. Done means deciding whether the style is sufficiently universal and, if so, updating the affected snippets consistently; the issue names no specific files or tests.