I've got a simple but tough problem : Texmaker does not recognize `\lewis` !

When I compile, it says : `Undefined control sequence. \lewis...`
I use chemfig of course. I've restarted my computer, a PC with Windows 10. I've tried `\Lewis`.

Can you help ?

```
\documentclass[a4paper, 10pt]{article} 
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc} 
\usepackage[french]{babel} 
\usepackage{graphicx} 
\usepackage{array} 
\usepackage{chemfig} 
\usepackage[version=4]{mhchem} 

\begin{document} 
    \lewis{2.,0} 
\end{document}

```