Documentation/gitformat-pack.txt: fix typo

e0d1bcf (multi-pack-index: add format details, 2018-07-12) describes
the MIDX's "PNAM" chunk as having entries which are "null-terminated
strings".

This is a typo, as strings are terminated with a NUL character, which is
a distinct concept from "NULL" or "null", which we typically reserve for
the void pointer to address 0.

Correct the documentation accordingly.

Signed-off-by: Taylor Blau <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

Documentation/gitformat-pack.txt

@@ -390,7 +390,7 @@ CHUNK LOOKUP:
 CHUNK DATA:
 
 	Packfile Names (ID: {'P', 'N', 'A', 'M'})
-	    Stores the packfile names as concatenated, null-terminated strings.
+	    Stores the packfile names as concatenated, NUL-terminated strings.
 	    Packfiles must be listed in lexicographic order for fast lookups by
 	    name. This is the only chunk not guaranteed to be a multiple of four
 	    bytes in length, so should be the last chunk for alignment reasons.