codec: travis: add support for testing against go 1.10

.travis.yml

@@ -4,6 +4,7 @@ go:
     - 1.7.x  # go testing suite support, which we use, was introduced in go 1.7
     - 1.8.x
     - 1.9.x
+    - 1.10.x
     - tip
 script:
     - go test -tags "alltests" -run Suite -coverprofile coverage.txt github.com/ugorji/go/codec