ci: fix travis.yml so that failure is captured properly

subtle errors in the config were causing test failures to be ignored

.travis.yml

@@ -6,5 +6,5 @@ go:
   - tip
 
 script:
-  - go test -bench=. -v ./... | grep -v 'no test files'
-  - pushd samples && find . -name "*.go" -exec go build {} \; && popd
+  - go test -bench=. -v ./... | grep -v 'no test files' ; test ${PIPESTATUS[0]} -eq 0
+  - cd samples; find . -name "*.go" -print0 | xargs -0 -n1 go build