refactor(docker): Update compose files (#1409)

* refactor(docker): Rename compose files

* refactor(docker): Remove obsolete version attribute

.examples/docker-compose-mattermost/compose.yaml

@@ -1,4 +1,3 @@
-version: "3.9"
 services:
   gatus:
     container_name: gatus

.examples/docker-compose-mtls/compose.yaml

@@ -1,4 +1,3 @@
-version: "3.9"
 services:
   nginx:
     image: nginx:stable

.examples/docker-compose-multiple-config-files/compose.yaml

@@ -1,4 +1,3 @@
-version: "3.8"
 services:
   gatus:
     image: twinproduction/gatus:latest

.examples/docker-compose-postgres-storage/compose.yaml

@@ -1,4 +1,3 @@
-version: "3.9"
 services:
   postgres:
     image: postgres

.examples/docker-compose-sqlite-storage/compose.yaml

@@ -1,4 +1,3 @@
-version: "3.9"
 services:
   gatus:
     image: twinproduction/gatus:latest

.examples/docker-compose/compose.yaml

@@ -1,4 +1,3 @@
-version: "3.8"
 services:
   gatus:
     image: twinproduction/gatus:latest