More descriptive steps + ensure Cask is found on path

See https://circleci.com/docs/2.0/env-vars/#using-bash_env-to-set-environment-variables

.circleci/config.yml

@@ -4,11 +4,21 @@ version: 2.0
 default: &default-steps
   steps:
     - checkout
-    - run: apt-get update
-    - run: apt-get install -y openjdk-8-jre make python git
-    - run: curl -fsSL https://raw.githubusercontent.com/cask/cask/master/go | python
-    - run: export PATH="/root/.cask/bin:$PATH"
-    - run: make
+    - run:
+        name: Update APT packages
+        command: apt-get update
+    - run:
+        name: Install prerequisites
+        command: apt-get install -y openjdk-8-jre make python git
+    - run:
+        name: Install cask
+        command: curl -fsSL https://raw.githubusercontent.com/cask/cask/master/go | python
+    - run:
+        name: Make Cask available on the path
+        command: echo 'export PATH="/root/.cask/bin:$PATH"' >> $BASH_ENV
+    - run:
+        name: Run the tests
+        command: make
 
 # Enumerated list of Emacs versions
 jobs: