Convert a glob string to a regular expressions.

 // Looking for all the `ts` files:
 walkSync(".", {
   match: [globToRegExp("*.ts")]
 });

 Looking for all the `.json` files in any subfolder:
 walkSync(".", {
   match: [globToRegExp(join("a", "**", "*.json"), {
     extended: true,
     globstar: true
   })]
 });