Pre-commit fixes.

With the updated hooks, address some newly found issues:
- Sort Python imports with isort.
- Don't cache pip packages in the container image.

Dockerfile

 FROM registry.hub.docker.com/library/python:3.9-alpine3.14
 WORKDIR /app
 COPY requirements.txt ./
-RUN pip install -r requirements.txt
+RUN pip install -r --no-cache-dir requirements.txt
 COPY * ./
 EXPOSE 8080
 ENV FORWARDED_ALLOW_IPS "*"

app.py

@@ -3,10 +3,10 @@
 
 import json
 import os
+
 import docker
 from flask import Flask, request
 
-
 app = Flask(__name__)
 client = docker.from_env()