Update Travis to use modern versions of Go

Author: bentranter

.travis.yml

@@ -1,9 +1,11 @@
 language: go
 
 go:
-  - 1.4
-  - 1.5
-  - 1.6
+  - 1.7
+  - 1.8
+  - 1.9
+  - "1.10"
+  - tip
 
 install:
   - go get -t ./...