Add initial Drone CI config

.drone.yml

@@ -0,0 +1,14 @@
+kind: pipeline
+type: docker
+name: CI build
+
+steps:
+  - name: rspec
+    image: guildeducation/rails:2.7.1-12.19.0
+    commands:
+      - bundle install
+      - yarn install
+      - bundle exec rspec
+    when:
+      branch:
+        - master