Calculate bytesize of chunk properly

> At v0.12 or ealier, `chunk.size` return bytesize. At v0.14,
> `chunk.size` returns the # of events in the chunk, not bytesize (and
> `chunk.bytesize` is added).

test/plugin/test_compressor.rb

@@ -46,7 +46,8 @@ def test_compress
       io = Tempfile.new("snappy-")
       @compressor.compress(chunk, io)
       io.open
-      assert(chunk.size > io.read.bytesize)
+      chunk_bytesize = chunk.respond_to?(:bytesize) ? chunk.bytesize : chunk.size
+      assert(chunk_bytesize > io.read.bytesize)
       io.rewind
       reader = ::Snappy::Reader.new(io)
       assert_equal(chunk.read, reader.read)