travis: update go versions

.travis.yml

@@ -4,10 +4,11 @@ install:
   - go get -d -t -v ./... && go build -v ./...
 
 go:
-  - 1.5
-  - 1.6
-  - 1.7
-  - 1.8
+  - 1.5.x
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - 1.9.x
   - tip
 
 script:
@@ -15,4 +16,4 @@ script:
   - go test -v -coverprofile=coverage.txt -covermode=atomic
 
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)