Update python Docker tag (GoogleCloudPlatform#2785)

Author: renovate-bot

appengine/flexible/tasks/Dockerfile

@@ -1,6 +1,6 @@
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy local code to the container image.
 ENV APP_HOME /app

cloud-sql/mysql/sqlalchemy/Dockerfile

@@ -14,7 +14,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy application dependency manifests to the container image.
 # Copying this separately prevents re-running pip install on every code change.

cloud-sql/postgres/sqlalchemy/Dockerfile

@@ -14,7 +14,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy application dependency manifests to the container image.
 # Copying this separately prevents re-running pip install on every code change.

run/hello-broken/Dockerfile

@@ -16,7 +16,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy application dependency manifests to the container image.
 # Copying this separately prevents re-running pip install on every code change.

run/image-processing/Dockerfile

@@ -14,7 +14,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy application dependency manifests to the container image.
 # Copying this separately prevents re-running pip install on every code change.

run/logging-manual/Dockerfile

@@ -14,7 +14,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy application dependency manifests to the container image.
 # Copying this separately prevents re-running pip install on every code change.

run/pubsub/Dockerfile

@@ -16,7 +16,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # Copy application dependency manifests to the container image.
 # Copying this separately prevents re-running pip install on every code change.

run/system-package/Dockerfile

@@ -14,7 +14,7 @@
 
 # Use the official Python image.
 # https://hub.docker.com/_/python
-FROM python:3.7
+FROM python:3.8
 
 # [START run_system_package_ubuntu]
 RUN apt-get update -y && apt-get install -y \

trace/cloud-trace-demo-app/app/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.6.0
+FROM python:3.8.0b1
 
 RUN pip3 install --upgrade pip