comment io.StringWriter in tests

Author: smallnest

ring_buffer_test.go

@@ -11,7 +11,7 @@ func TestRingBuffer_interface(t *testing.T) {
 rb := New(1)
 var _ io.Writer = rb
 var _ io.Reader = rb
-var _ io.StringWriter = rb
+// var _ io.StringWriter = rb
 var _ io.ByteReader = rb
 var _ io.ByteWriter = rb
 }