Describe the bug
When running gh-md-toc --insert ./Readme.md i get

You don't have <!--ts--> or <!--te--> in your file...exiting

It seems this comes down to this command not working

kyle@Emilys-MacBook-Pro kubectl-opslevel % grep -Fxq "<\!--ts-->" Readme.md

but this one does

kyle@Emilys-MacBook-Pro kubectl-opslevel % grep -F "<\!--ts-->" Readme.md
<!--ts-->

Notice the arguments to grep. I'm using zsh (the macos native shell now - not sure if that has an impact)