drop 1.4, add tip, make golint error.

.travis.yml

@@ -1,13 +1,13 @@
 language: go
 go:
-    - 1.4
     - 1.5
     - 1.6
+    - tip
 install:
     - go get github.com/bwmarrin/discordgo
     - go get -v .
     - go get -v github.com/golang/lint/golint
 script:
     - go vet -x ./...
-    - golint ./...
+    - golint -set_exit_status ./...
     - go test -v -race ./...