Run "make test" on Travis CI

"make" doesn't compile *_test.go, but "make test" does.

121afa3 introduced
ProcessState.ExitCode which is not available in Go 1.11.

Signed-off-by: Kazuyoshi Kato <[email protected]>

Author: kzys

.travis.yml

@@ -13,5 +13,7 @@ install:
   - make deps
 
 script:
+  # "make" must be happening before "make lint" to download dependencies
   - make
   - make lint
+  - make test