Documentation: Spelling fix in protocol-capabilities.txt

Signed-off-by: NFredrik Skolmli <fredrik@frsk.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/technical/protocol-capabilities.txt

@@ -119,7 +119,7 @@ both.
 ofs-delta
 ---------
 
-Server can send, and client understand PACKv2 with delta refering to
+Server can send, and client understand PACKv2 with delta referring to
 its base by position in pack rather than by an obj-id.  That is, they can
 send/read OBJ_OFS_DELTA (aka type 6) in a packfile.