Added Lucas to mantainers list. (thanos-io#1732)

Signed-off-by: Bartek Plotka <[email protected]>

MAINTAINERS.md

@@ -8,6 +8,7 @@
 | Giedrius Statkevičius | [email protected] | `@Giedrius Statkevičius` | [@GiedriusS](https://github.com/GiedriusS)  | AdForm            |
 | Povilas Versockas     | [email protected]  | `@povilasv`              | [@povilasv](https://github.com/povilasv)    | Utility Warehouse |
 | Matthias Loibl        | [email protected] | `@metalmatze`            | [@metalmatze](https://github.com/metalmatze)| Red Hat           |
+| Lucas Servén Marín    | [email protected]      |  `@squat`                  | [@squat](https://github.com/squat)          | Red Hat           |
 
 We are bunch of people from different companies with various interests and skills.
 We are from different parts of Europe: Germany, Lithuania, Poland and UK.