travis: update to go versions to 1.8.5, 1.9.2

Author: cfromknecht

.travis.yml

@@ -1,7 +1,7 @@
 language: go
 go:
-  - 1.6.3
-  - 1.7
+  - 1.8.5
+  - 1.9.2
 sudo: false
 install:
   - go get -v github.com/lightningnetwork/lightning-onion