update go version at travis-ci

Signed-off-by: Máximo Cuadros <mcuadros@gmail.com>

.travis.yml

@@ -1,8 +1,12 @@
 language: go
 go:
-  - 1.6.x
   - 1.7.x
-# - master
+  - 1.8.x
+  - tip
+
+matrix:
+  allow_failures:
+    - go: tip
 
 # `make ci` uses Docker.
 sudo: required

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.7.4
+FROM golang:1.8.0
 
 # libseccomp in jessie is not _quite_ new enough -- need backports version
 RUN echo 'deb http://httpredir.debian.org/debian jessie-backports main' > /etc/apt/sources.list.d/backports.list