Added drone pipeline that automaticly runs on prs (or at least it should)

ref #23

.drone.yml

@@ -0,0 +1,13 @@
+---
+kind: pipeline
+name: tests:latest
+
+steps:
+- name: run tests
+  image: node:alpine
+  commands:
+  - npm install
+  - npm test
+trigger:
+  event:
+  - pull_request