fix(docker compose): set minimum compose version as '3' (#1677)

- matches the minimum version for our dependencies file ('3')
- healthcheck was introduced in 2.1, and healthcheck.start_period in 2.3, so >=2.3 was minimum

docker-compose-speckle.yml

@@ -1,4 +1,4 @@
-version: '2'
+version: '3'
 services:
   speckle-frontend:
     build:

utils/1click_image_scripts/template-docker-compose.yml

@@ -1,4 +1,4 @@
-version: '2'
+version: '3'
 services:
   ####
   # Speckle Server dependencies