[documentation-fix] Typo in documentation for (exit)

[Jay Bosamiya]

The documentation we get for exit using (documentation 'exit 'function) seems to have a typo in the line "Recursive calls to EXIT cause EXIT to behave as it ABORT was true."

I believe it must say "Recursive calls to EXIT cause EXIT to behave as if ABORT was true."

(Notice the s/it/if/)

sbcl --version: SBCL 1.3.20
(Downloaded binary recently from website)

PFA: Patch to fix the typo

[Stas Boukarev (stassats)]

In 5ae874471042ff135af7794cce7c5ac771f626ba