Add Drone configuration.

.drone.yml

@@ -0,0 +1,12 @@
+kind: pipeline
+name: default
+
+steps:
+  - name: test
+    image: rust
+    commands:
+      - cargo fmt --check
+      - cargo build --all
+      - cargo build --examples --all
+      - cargo test --verbose --all
+      - cargo clippy

.travis.yml

@@ -1,4 +0,0 @@
-language: rust
-rust:
-  - stable
-  - beta