Avoid using -i argument to go test

Since Golang 1.10, this option should no longer be required:

https://golang.org/doc/go1.10#build

> The old advice to add the -i flag for speed, as in go build -i or go
test -i, is no longer necessary: builds run just as fast without -i. For
more details, see go help cache.

Furthermore, it creates issues like the below when running ginkgo
against a snap-installed version of Golang 1.10 on Ubuntu 18.04:

  $ ginkgo build
  Compiling test...
  Failed to compile test:

  go test runtime/cgo: open /snap/go/2130/pkg/linux_amd64/runtime/cgo.a: read-only file system

ginkgo/testrunner/test_runner.go

@@ -64,7 +64,7 @@ func (t *TestRunner) Compile() error {
 }
 
 func (t *TestRunner) BuildArgs(path string) []string {
-	args := []string{"test", "-c", "-i", "-o", path, t.Suite.Path}
+	args := []string{"test", "-c", "-o", path, t.Suite.Path}
 
 	if t.getCoverMode() != "" {
 		args = append(args, "-cover", fmt.Sprintf("-covermode=%s", t.getCoverMode()))

ginkgo/testrunner/test_runner_test.go

@@ -39,7 +39,6 @@ var _ = Describe("TestRunner", func() {
 		Ω(args).Should(Equal([]string{
 			"test",
 			"-c",
-			"-i",
 			"-o",
 			".",
 			"",