Allow Go tip to fail on TravisCI

.travis.yml

@@ -18,27 +18,30 @@ go:
   - tip
 
 matrix:
-    exclude:
-        - os: osx
-          go: 1.2.x
-        - os: osx
-          go: 1.3.x
-        - os: osx
-          go: 1.4
-        - os: osx
-          go: 1.5.x
-        - os: osx
-          go: 1.6.x
+  allow_failures:
+    - go: tip
+
+  exclude:
+    - os: osx
+      go: 1.2.x
+    - os: osx
+      go: 1.3.x
+    - os: osx
+      go: 1.4
+    - os: osx
+      go: 1.5.x
+    - os: osx
+      go: 1.6.x
 
 sudo: required
 before_install:
-  - if [[ $TRAVIS_GO_VERSION == 1.9* ]]; then go get github.com/axw/gocov/gocov github.com/mattn/goveralls; fi
+  - if [[ $TRAVIS_GO_VERSION == 1.12* ]]; then go get github.com/axw/gocov/gocov github.com/mattn/goveralls; fi
   - sudo apt-get update -qq
   - sudo apt-get install -y cracklib-runtime
 
 script:
   - go test -v -tags ci ./...
-  - if [[ $TRAVIS_GO_VERSION == 1.9* ]]; then $GOPATH/bin/goveralls -service=travis-ci; fi
+  - if [[ $TRAVIS_GO_VERSION == 1.12* ]]; then $GOPATH/bin/goveralls -service=travis-ci; fi
 
 notifications:
   email: