Update config.yml

Author: gkorland

.circleci/config.yml

@@ -7,6 +7,10 @@ jobs:
 
     steps:
       - checkout
+      - run:
+          name: Install prerequisite
+          command: >-
+            apt-get update; apt-get install -y clang
       - run:
           name: Install Submodules
           command: git submodule add  https://github.com/RedisLabsModules/redismodule-rs