CI: Pin Travis golang version

Travis appears to be providing a version of golang that is too old for
https://mvdan.cc/xurls/cmd/xurls, which is used by the CI scripts in the
tests repo.

See:

- kata-containers/runtime#744
- kata-containers/tests#843 (comment)

Fixes kata-containers#281.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

.travis.yml

@@ -9,6 +9,9 @@ dist: trusty
 
 language: bash
 
+go:
+  - "1.10.x"
+
 before_script:
   - ".ci/setup.sh"