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

[Dmitry Gutov <dgutov@yandex.ru>]

Hi Steve,

On 03.05.2021 04:01, Steve Purcell wrote:
> Both these methods can be called without arguments, so the font
> locking of "bare" calls to either is incorrect.  The fix is to
> font-lock them as for other kernel methods which accepts zero or more
> arguments.

Is that important? Like, is anybody likely to call either without args? 
font-lock is not a precise facility (that anything depends on), so we 
can afford to be wrong in 0.01% cases.

If we institute this principle, I suppose we'll need to do this for all 
functions that can work without args? In my testing, that's also:

p, open, loop, warn, print

Also note that your title says 'printf', but the patch said 'print'.