Increase /var/lib/tor tmpfs size to 12MB (#693)

After an uptime of 109 days, the usage of /var/lib/tor was still 10.9 MB. A
reply in issue #648 reported a higher usage, which was fixed by setting the
size a bit higher (12MB instead of 11MB).

docker-compose.yml

@@ -18,7 +18,7 @@ services:
       - ALL
     tmpfs:
       - /config/:size=10M,uid=927,gid=927,mode=1700
-      - /var/lib/tor/:size=10M,uid=927,gid=927,mode=1700
+      - /var/lib/tor/:size=15M,uid=927,gid=927,mode=1700
       - /run/tor/:size=1M,uid=927,gid=927,mode=1700
     #environment: # Uncomment to configure environment variables
       # Basic auth configuration, uncomment to enable