travis: refresh the pipeline (#77)

- incorporate go modules
- use 1.x to make sure we always use latest version of go
- enable the race detector in tests

Author: fsouza

.travis.yml

@@ -1,6 +1,10 @@
 language: go
-
 go:
-  - 1.7
-  - 1.8
+  - 1.x
   - tip
+env:
+  - GO111MODULE=on
+install:
+  - go mod download
+script:
+  - go test -race -v