etherpad,jigasi: fix compose file version

They all need to match if we want to launch them together.

etherpad.yml

@@ -1,4 +1,4 @@
-version: '3'
+version: '3.5'
 
 services:
     # Etherpad: real-time collaborative document editing

jigasi.yml

@@ -1,4 +1,4 @@
-version: '3'
+version: '3.5'
 
 services:
     # SIP gateway (audio)