fix: add missing awk to get number of lines in key file

plugins/ssh-keys/subcommands/add

@@ -28,7 +28,7 @@ add_keys() {
     dokku_log_fail "Empty key was specified"
   fi
 
-  local count="$(wc -l "$KEY_FILE")"
+  local count="$(wc -l "$KEY_FILE" | awk '{ print $1; }')"
   [[ "$count" -eq 1 ]] || dokku_log_fail "Too many keys provided, set one per invocation of dokku ssh-keys:add <NAME> <KEY_FILE>"
   ssh-keygen -lf "$KEY_FILE" &>/dev/null || dokku_log_fail "Key specified in is not a valid ssh public key"
   create_ssh_key_file