Fix error message when user passes a single array argument (#468)

Author: ehmicky

lib/command.js

@@ -11,7 +11,7 @@ const NO_ESCAPE_REGEXP = /^[\w.-]+$/;
 const DOUBLE_QUOTES_REGEXP = /"/g;
 
 const escapeArg = arg => {
-	if (NO_ESCAPE_REGEXP.test(arg)) {
+	if (typeof arg !== 'string' || NO_ESCAPE_REGEXP.test(arg)) {
 		return arg;
 	}