Fix broken links to .env and docker-compose.yml files (#3989)

Author: leemthompo

deploy-manage/deploy/self-managed/install-elasticsearch-docker-compose.md

@@ -23,8 +23,8 @@ Use Docker Compose to start a three-node {{es}} cluster with {{kib}}. Docker Com
 2. Create or navigate to an empty directory for the project.
 3. Download and save the following files in the project directory:
 
-    * [`.env`](https://github.com/elastic/elasticsearch/blob/master/docs/reference/setup/install/docker/.env)
-    * [`docker-compose.yml`](https://github.com/elastic/elasticsearch/blob/master/docs/reference/setup/install/docker/docker-compose.yml)
+    * [`.env`](https://github.com/elastic/elasticsearch/blob/main/docs/reference/setup/install/docker/.env)
+    * [`docker-compose.yml`](https://github.com/elastic/elasticsearch/blob/main/docs/reference/setup/install/docker/docker-compose.yml)
 
 4. In the `.env` file, specify a password for the `ELASTIC_PASSWORD` and `KIBANA_PASSWORD` variables.
 
@@ -104,4 +104,4 @@ docker-compose down -v
 
 ## Next steps [_next_steps_6]
 
-You now have a test {{es}} environment set up. Before you start serious development or go into production with {{es}}, review the [requirements and recommendations](/deploy-manage/deploy/self-managed/install-elasticsearch-docker-prod.md) to apply when running {{es}} in Docker in production.
+You now have a test {{es}} environment set up. Before you start serious development or go into production with {{es}}, review the [requirements and recommendations](/deploy-manage/deploy/self-managed/install-elasticsearch-docker-prod.md) to apply when running {{es}} in Docker in production.