test against Go 1.10

.travis.yml

@@ -4,6 +4,7 @@ go:
   - 1.7.x
   - 1.8.x
   - 1.9.x
+  - 1.10.x
   - master
 
 go_import_path: gopkg.in/jcmturner/gokrb5.v4