Bump baseimage to python3.8

Related-bug: PRODX-7695
Change-Id: Ic5f19fa759c0ac1ddb69b9bdbf6add309d9d82a2
diff --git a/Dockerfile b/Dockerfile
index 876275f..41e4859 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM python:3.7-slim
+FROM python:3.8-slim
 
 WORKDIR /usr/src/app