chore: bump to release version 1.6.12

DESCRIPTION

 Package: airGR
 Type: Package
 Title: Suite of GR Hydrological Models for Precipitation-Runoff Modelling
-Version: 1.6.11
-Date: 2021-04-26
+Version: 1.6.12
+Date: 2021-04-27
 Authors@R: c(
   person("Laurent", "Coron", role = c("aut", "trl"), comment = c(ORCID = "0000-0002-1503-6204")),
   person("Olivier", "Delaigue", role = c("aut", "cre"), comment = c(ORCID = "0000-0002-7668-8468"), email = "airGR@inrae.fr"),

NEWS.md

@@ -2,7 +2,7 @@
 
 
 
-### 1.6.11 Release Notes (2021-04-26)
+### 1.6.12 Release Notes (2021-04-27)
 
 #### New features