Replace Travis with Drone CI

.drone.yml

@@ -0,0 +1,14 @@
+---
+kind: pipeline
+type: docker
+name: default
+
+steps:
+  - name: test
+    image: golang:1.18rc1-bullseye
+    commands:
+      - DEBIAN_FRONTEND=noninteractive apt update
+      - DEBIAN_FRONTEND=noninteractive apt install -y libflac-dev
+      - go test -cover -v
+
+...

.travis.yml

@@ -1,13 +0,0 @@
-language: go
-go:
-    - "1.6"
-addons:
-  apt:
-    packages:
-      - libflac-dev
-before_install:
-  - go get github.com/axw/gocov/gocov
-  - go get github.com/mattn/goveralls
-  - if ! go get github.com/golang/tools/cmd/cover; then go get golang.org/x/tools/cmd/cover; fi
-script:
-  - $HOME/gopath/bin/goveralls -service=travis-ci