Use Docker image, bump Python

Dockerfile

@@ -1,16 +1,5 @@
 # Container image that runs your code
-FROM ubuntu:18.04
-
-RUN apt-get update \
-    && apt-get install -y \
-    build-essential \
-    python3-pip \
-    python3.6 \
-    git \
-    && python3 -m pip install --upgrade pip \
-    && python3 -m pip install --upgrade setuptools \
-    && python3 -m pip install --upgrade wheel \
-    && python3 -m pip install PyGithub
+FROM quay.io/spacetelescope/astropy-actions-docker:0.1
 
 # Copies code file action repository to the filesystem path `/` of the container
 COPY entrypoint.sh /entrypoint.sh

entrypoint.sh

@@ -1,6 +1,6 @@
 #!/bin/bash -l
 
-PYTHON=$(which python3.6)
+PYTHON=$(which python3.8)
 echo "PYTHON=${PYTHON}"
 
 $PYTHON /special_day.py