Clarify cap option is -c

sbotc.1

@@ -9,7 +9,7 @@
 .Nm
 .Op Fl j
 .Op Fl T
-.Op Fl a Ar cap
+.Op Fl c Ar cap
 .Op Fl s Ar host
 .Op Fl p Ar port
 .Op Fl k Ar key

sbotc.c

@@ -95,7 +95,7 @@ static const unsigned char ssb_cap[] = {
 };
 
 static void usage() {
-	fputs("usage: sbotc [-j] [-T] [-a <cap>] [-s <host>] [-p <port>] [-k <key>] [-K <keypair_seed>] \n"
+	fputs("usage: sbotc [-j] [-T] [-c <cap>] [-s <host>] [-p <port>] [-k <key>] [-K <keypair_seed>] \n"
 	      "             [-t <type>] <method> [<argument>...]\n", stderr);
 	exit(EXIT_FAILURE);
 }