Duplicate `adding` in `webgl-anti-patterns.md`
Duplicate `adding` in `webgl-anti-patterns.md`

Thanks for these great lessons! Found a typo and thought I'd send a PR as a thank you.
ichenjin/webgl-fundamentals,housekeeponline/webgl-fundamentals,ichenjin/webgl-fundamentals,ichenjin/webgl-fundamentals,housekeeponline/webgl-fundamentals,housekeeponline/webgl-fundamentals,ichenjin/webgl-fundamentals