An attempt to fix Travis CI builds and add modern Go targets

Author: iafan

.travis.yml

@@ -1,8 +1,12 @@
 language: go
+go_import_path: github.com/sourcegraph/syntaxhighlight
 go:
-  - 1.4
+  - 1.4.x
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - tip
 install:
-  - go get golang.org/x/tools/cmd/vet
   - go get -t -v ./...
 script:
   - diff -u <(echo -n) <(gofmt -d ./)