transport: fix capabilities calculation

This looks like a typo to me, from what i can see these lines were
added at the same time and because of how capabilities are calculated,
it's likely that this code will work in situations where these
capabilities were the last ones.

src/libgit2/transports/smart_protocol.c

@@ -207,13 +207,13 @@ int git_smart__detect_caps(git_pkt_ref *pkt, transport_smart_caps *caps, git_vec
 
 		if (!git__prefixcmp(ptr, GIT_CAP_WANT_TIP_SHA1)) {
 			caps->common = caps->want_tip_sha1 = 1;
-			ptr += strlen(GIT_CAP_DELETE_REFS);
+			ptr += strlen(GIT_CAP_WANT_TIP_SHA1);
 			continue;
 		}
 
 		if (!git__prefixcmp(ptr, GIT_CAP_WANT_REACHABLE_SHA1)) {
 			caps->common = caps->want_reachable_sha1 = 1;
-			ptr += strlen(GIT_CAP_DELETE_REFS);
+			ptr += strlen(GIT_CAP_WANT_REACHABLE_SHA1);
 			continue;
 		}