Update status to 'stable'

Author: JeffCarver

config.yaml

@@ -28,7 +28,7 @@ keywords: 'software, data, lesson, The Carpentries' # FIXME
 
 # Life cycle stage of the lesson
 # possible values: pre-alpha, alpha, beta, stable
-life_cycle: 'beta' 
+life_cycle: 'stable' 
 
 # License of the lesson
 license: 'CC-BY 4.0'