doc: fix want-capability separator

Unlike ref advertisement, client capabilities and the first want are
separated by SP, not NUL, in the implementation. Fix the documentation
to align with the implementation. pack-protocol.txt is already fixed.

Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/http-protocol.txt

@@ -338,11 +338,11 @@ server advertises capability `allow-tip-sha1-in-want` or
 		       request_end
   request_end       =  "0000" / "done"
 
-  want_list         =  PKT-LINE(want NUL cap_list LF)
+  want_list         =  PKT-LINE(want SP cap_list LF)
 		       *(want_pkt)
   want_pkt          =  PKT-LINE(want LF)
   want              =  "want" SP id
-  cap_list          =  *(SP capability) SP
+  cap_list          =  capability *(SP capability)
 
   have_list         =  *PKT-LINE("have" SP id LF)