cmd/go: fix build

The new semantics of split require the newline be present.
The test was stale.

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/182480043

src/cmd/go/generate.go

@@ -250,7 +250,7 @@ func isGoGenerate(buf []byte) bool {
 
 // split breaks the line into words, evaluating quoted
 // strings and evaluating environment variables.
-// The initial //go:generate element is dropped.
+// The initial //go:generate element is present in line.
 func (g *Generator) split(line string) []string {
 	// Parse line, obeying quoted strings.
 	var words []string

src/cmd/go/generate_test.go

@@ -40,7 +40,7 @@ func TestGenerateCommandParse(t *testing.T) {
 	}
 	g.setShorthand([]string{"-command", "yacc", "go", "tool", "yacc"})
 	for _, test := range splitTests {
-		got := g.split("//go:generate " + test.in)
+		got := g.split("//go:generate " + test.in + "\n")
 		if !reflect.DeepEqual(got, test.out) {
 			t.Errorf("split(%q): got %q expected %q", test.in, got, test.out)
 		}