Enable drone CI.

.drone.yml

@@ -0,0 +1,15 @@
+kind: pipeline
+type: docker
+name: default
+
+steps:
+  - name: test
+    image: maven:3.6-jdk-11
+    commands:
+      - mvn clean install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
+      - mvn test -B
+    when:
+      branch:
+        include:
+          - master
+          - feature/*