Compilation error on Ubuntu 20.10

[vnghia]

When compiling //tensorflow_io/core:python/ops/libtensorflow_io.so, it throws an error:

external/avro/impl/Zigzag.cc:66:1: error: 'size_t' does not name a type
   66 | size_t
      | ^~~~~~

gcc version

gcc (Ubuntu 10.2.0-13ubuntu1) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Releated to apache/avro#837

I think we need to bump avro to at least 1.10.1.

[yongtang]

@vnvo2409 Created a PR #1235 for the fix.