bug#28781: 25.3; Override erroneous "incorrect verb voice" from checkdoc

[Eli Zaretskii]

> From: Radon Rosborough <radon.neon@gmail.com>
> Date: Tue, 10 Oct 2017 10:52:18 -0700
> 
> I have the following definition:
> 
>     (defmacro straight--functionp (object)
>       "Non-nil if OBJECT, an unquoted symbol, evaluates to a function.

Try

    "Return non-nil if OBJECT, an unquoted symbol, evaluates to a function."

Or even

    "Return non-nil if OBJECT, evaluates to a function.
  OBJECT should be an unquoted symbol."