Update utils_test.go to allow running in read-only mode. (#91)

Restrict `os.OpenFile` to use just read flag, which allows to pass tests on the
systems like Guix with isolated read-only environment.

Author: Hellseher

utils_test.go

@@ -17,7 +17,7 @@ func TestUtilFuncs(t *testing.T) {
 	is.True(IsConsole(os.Stdout))
 	is.True(IsConsole(os.Stderr))
 	is.False(IsConsole(&bytes.Buffer{}))
-	ff, err := os.OpenFile("README.md", os.O_WRONLY, 0)
+	ff, err := os.OpenFile("README.md", os.O_RDONLY, 0)
 	is.NoError(err)
 	is.False(IsConsole(ff))