Update .travis.yml to have proper indentation

Author: Sander van Harmelen

.travis.yml

@@ -1,23 +1,23 @@
 dist: trusty
 sudo: required
 services:
-- docker
+  - docker
 language: go
 go:
   - "1.11.x"
 
 script:
-- make vet
-- make test
-- make website-test
+  - make vet
+  - make test
+  - make website-test
 
 env:
-- GO111MODULE=off
+  - GO111MODULE=off
 
 branches:
   only:
-  - master
+    - master
 matrix:
   fast_finish: true
   allow_failures:
-  - go: tip
+    - go: tip