CI: use go mod

Author: nanmu42

.travis.yml

@@ -1,7 +1,10 @@
 language: go
 
+env:
+  - GO111MODULE=on
+
 script:
-- go test -v -coverprofile=coverage.txt -covermode=count ./...
+  - go test -v -coverprofile=coverage.txt -covermode=count ./...
 
 after_success:
-- bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)