Update Travis CI to build against the latest Go (#167)

* Update Travis CI to build against the latest Go
* Update vet to only run on the latest Go version.

Author: elithrar

.travis.yml

@@ -3,11 +3,17 @@ sudo: false
 
 matrix:
   include:
-    - go: 1.3
-    - go: 1.4
-    - go: 1.5
-    - go: 1.6
-    - go: 1.7
+    - go: 1.3.x
+    - go: 1.4.x
+    - go: 1.5.x
+    - go: 1.6.x
+    - go: 1.7.x
+    - go: 1.8.x
+    - go: 1.9.x
+    - go: 1.10.x
+    - go: 1.11.x
+    - go: 1.x
+      env: LATEST=true
     - go: tip
   allow_failures:
     - go: tip
@@ -18,5 +24,5 @@ install:
 script:
   - go get -t -v ./...
   - diff -u <(echo -n) <(gofmt -d .)
-  - go vet $(go list ./... | grep -v /vendor/)
+  - if [[ "$LATEST" = true ]]; then go vet $(go list ./... | grep -v /vendor/); fi
   - go test -v -race ./...