Add Image Version to Docker-Compose to pull the relevant image (alshe…

…divat#2740)

This is to address 
- alshedivat#2733 

Since a lot of times, the only problem is that docker image is not
consistent with the build. We have to somehow incorporate image version
into repository.

I don't insist to provide it this way. Maybe there are other automatic
ways which are better.

We can also calculate the relevant tag from git.

docker-compose.yml

@@ -1,7 +1,7 @@
 # this file uses prebuilt image in dockerhub
 services:
   jekyll:
-    image: amirpourmand/al-folio:latest
+    image: amirpourmand/al-folio:v0.12.0
     build: .
     ports:
       - 8080:8080