build image before testing

Author: jatinkatyal13

.travis.yml

@@ -10,6 +10,7 @@ before_install:
 
 install:
   - npm install -D
+  - docker build . -t codingblocks/judge-taskmaster
   - docker pull codingblocks/judge-worker-c
   - docker pull codingblocks/judge-worker-cpp
   - docker pull codingblocks/judge-worker-csharp