ci: smoke-test the release script

To make sure that `make release` doesn't suddenly break after we've cut
a release, smoke-test the release scripts. The script won't fail if GPG
keys aren't found, so running in CI shouldn't be a huge issue.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

.travis.yml

@@ -30,4 +30,4 @@ before_install:
 script:
   - git-validation -run DCO,short-subject -v
   - make BUILDTAGS="${BUILDTAGS}"
-  - make BUILDTAGS="${BUILDTAGS}" clean validate test
+  - make BUILDTAGS="${BUILDTAGS}" clean ci

Makefile

@@ -115,7 +115,7 @@ validate:
 	script/validate-gofmt
 	$(GO) vet $(allpackages)
 
-ci: validate localtest
+ci: validate test release
 
 # memoize allpackages, so that it's executed only once and only if used
 _allpackages = $(shell $(GO) list ./... | grep -v vendor)