fix: correctly render the command name in the help text

Previously the help text failed to render the name of the script being executed in the help text.

The issue was detected by shellcheck, this commit also includes another minor fix detected by ShellCheck.

Closes #16

wait-for

@@ -36,7 +36,7 @@ usage() {
   exitcode="$1"
   cat << USAGE >&2
 Usage:
-  $cmdname host:port|url [-t timeout] [-- command args]
+  $0 host:port|url [-t timeout] [-- command args]
   -q | --quiet                        Do not output any status messages
   -t TIMEOUT | --timeout=timeout      Timeout in seconds, zero for no timeout
   -- COMMAND ARGS                     Execute command with args after the test finishes
@@ -168,7 +168,7 @@ fi
 
 case "$PROTOCOL" in
   tcp)
-    if [ "$HOST" = "" -o "$PORT" = "" ]; then
+    if [ "$HOST" = "" ] || [ "$PORT" = "" ]; then
       echoerr "Error: you need to provide a host and port to test."
       usage 2
     fi