Upgrade python image to v3.8 as v3.7 is broken and un supported since 5 months ago

Author: lvarin

Dockerfile

@@ -1,8 +1,8 @@
 ##### BASE IMAGE #####
-FROM python:3.7-slim-stretch
+FROM python:3.8-slim
 
 ##### METADATA #####
-LABEL base.image="python:3.6-slim-stretch"
+LABEL base.image="python:3.8-slim"
 LABEL version="1.1"
 LABEL software="cwl-WES"
 LABEL software.version="1.0"