config: Add es-MX to language code mapping

Change-Id: Ic55059fbd70ce6c7982d1877413bab10bb51d814
diff --git a/crowdin/crowdin_cm-12.1_aosp.yaml b/crowdin/crowdin_cm-12.1_aosp.yaml
index 903e5dc..31f2a88 100644
--- a/crowdin/crowdin_cm-12.1_aosp.yaml
+++ b/crowdin/crowdin_cm-12.1_aosp.yaml
@@ -36,6 +36,7 @@
         be: be
         cy: cy
         en-PT: en-rPT
+        es-MX: es-rMX
         eo: eo
         fy-NL: fy-rNL
         ku: ku