Bump docs environment to python 3.7 (testcontainers#3871)

Author: xp-vit

docker-compose.yml

@@ -2,7 +2,7 @@ version: "3.7"
 
 services:
   docs:
-    image: python:3.6
+    image: python:3.7
     command: sh -c "pip install -r requirements.txt && mkdocs serve -a 0.0.0.0:8000"
     working_dir: /docs
     volumes:

docs/contributing_docs.md

@@ -15,7 +15,7 @@ The root of the project contains a `docker-compose.yml` file. Simply run `docker
 
 ### Using Python locally
 
-* Ensure that you have Python 3.6.0 or higher.
+* Ensure that you have Python 3.7.0 or higher.
 * Set up a virtualenv and run `pip install -r requirements.txt` in the `testcontainers-java` root directory.
 * Once Python dependencies have been installed, run `mkdocs serve` to start a local auto-updating MkDocs server.