Add Mathieu Lonjaret to maintainers

Author: emilevauge

docs/content/contributing/maintainers.md

@@ -16,6 +16,7 @@
 * Gérald Croës [@geraldcroes](https://github.com/geraldcroes)
 * Jean-Baptiste Doumenjou [@jbdoumenjou](https://github.com/jbdoumenjou)
 * Damien Duportal [@dduportal](https://github.com/dduportal)
+* Mathieu Lonjaret [@mpl](https://github.com/mpl)
 
 ## Contributions Daily Meeting