ci: update base image and install the latest clang to it

.circleci/config.yml

@@ -3,11 +3,7 @@ version: 2
 defaults: &defaults
  working_directory: /tmp/project
  docker:
-   - image: walberla/buildenv-ubuntu-clang:3.8
-     environment:
-       CIRCLE_BUILD_IMAGE: ubuntu
-       ATOM_CHANNEL: stable
-       DISPLAY: :99
+   - image: arcanemagus/atom-docker-ci:stable
 
 jobs:
   checkout_code:
@@ -42,10 +38,9 @@ jobs:
       - run:
           name: Update APT
           command: apt-get update
-      # Install some pre-requisite packages and missing dependencies from the atom package
       - run:
-          name: Atom Prerequisites
-          command: apt-get --assume-yes --quiet --no-install-suggests --no-install-recommends install sudo xvfb libxss1 libasound2
+          name: Install Clang
+          command: apt-get --assume-yes --quiet --no-install-suggests --no-install-recommends install clang
       # Fire up a VFB to run Atom in
       - run:
           name: Create VFB for Atom to run in
@@ -62,19 +57,17 @@ jobs:
 
   beta:
     <<: *defaults
-    environment:
-      ATOM_CHANNEL: beta
+    image: arcanemagus/atom-docker-ci:beta
     steps:
       # Restore project state
       - attach_workspace:
           at: /tmp
       - run:
           name: Update APT
           command: apt-get update
-      # Install some pre-requisite packages and missing dependencies from the atom package
       - run:
-          name: Atom Prerequisites
-          command: apt-get --assume-yes --quiet --no-install-suggests --no-install-recommends install sudo xvfb libxss1 libasound2
+          name: Install Clang
+          command: apt-get --assume-yes --quiet --no-install-suggests --no-install-recommends install clang
       # Fire up a VFB to run Atom in
       - run:
           name: Create VFB for Atom to run in