travis: separate go vet, put it first

Since go vet is much quicker than running tests, call it first
(no sense in doing further tests if it fails).

Also, put it to a separate line, as the travis output is more
comprehensible this way.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

.travis.yml

@@ -20,4 +20,5 @@ install:
 
 script:
   - GO111MODULE="on" go mod tidy && git diff --exit-code go.mod go.sum
-  - ginkgo -r --randomizeAllSpecs --randomizeSuites --race --trace && go vet
+  - go vet
+  - ginkgo -r --randomizeAllSpecs --randomizeSuites --race --trace