bug#48180: ruby-mode.el: fix font lock for puts and printf

[Dmitry Gutov]

On 03.05.2021 23:31, Steve Purcell wrote:
> > It always bothered me that in ruby-mode highlighting was broken for printing
> > without arguments, but I had no time to investigate.  Now finally this is fixed.
> > Maybe some other printing like "p" could be fixed as well, but the
> > already fixed "puts" and "print" is an improvement.
>
> Yes, it’s actually pretty common to just use “puts” without args to print an 
> empty line.

Very good, then.