Use String.indexOf() instead of RegExp

Author: aweebit

lib/option.js

@@ -24,9 +24,11 @@ class Option {
     this.long = optionFlags.longFlag;
     this.strictOptionalHelpTerm = null;
     if (this.optional) {
-      const { 0: argument, index } = flags.match(/\[.*\]/);
+      const indexStart = flags.indexOf('[');
+      const indexEnd = indexStart + flags.slice(indexStart).indexOf(']') + 1;
+      const argument = flags.slice(indexStart, indexEnd);
       this.strictOptionalHelpTerm = (
-        flags.slice(0, index) + flags.slice(index + argument.length)
+        flags.slice(0, indexStart) + flags.slice(indexEnd)
       );
       if (this.short) {
         this.strictOptionalHelpTerm = this.strictOptionalHelpTerm