Migrate circleci configuration to 2.0

.circleci/config.yml

@@ -0,0 +1,25 @@
+version: 2
+jobs:
+  build:
+    docker:
+      - image: circleci/elixir:1.6
+        environment:
+          MIX_ENV: test
+
+    working_directory: ~/repo
+    steps:
+      - checkout
+      - run: mix local.hex --force  # install Hex locally (without prompt)
+      - run: mix local.rebar --force  # fetch a copy of rebar (without prompt)
+
+      - restore_cache:
+          keys:
+            - mix-cache-{{ checksum "mix.lock" }}
+
+      - run: mix do deps.get
+      - save_cache:
+          key: mix-cache-{{ checksum "mix.lock" }}
+          paths: "deps"
+
+      - run: mix test
+      - run: MIX_ENV=prod mix compile