Go Version 1.16

v1.16.0

Update to 1.16

Go Version 1.15.2

Use ubuntu xenial as build base

See gotify/server#361

Go Version 1.14.2

v1.14.2

Use golang:*-stretch

Go Version 1.13.1

v1.13.1

Use golang:*-stretch

Go Version 1.12.0

v1.12.0

Add travis-ci build script

Go Version 1.11.5

v1.11.5

Add travis-ci build script