Add support for js commas

[bmteller]

No description provided.

[bmteller]

There was 1 failing test but this is unrelated and was already failing on the 1.1.2 tag.

  1) test copying strings on decode (Jason.DecodeTest)
     test/decode_test.exs:88
     Assertion with == failed
     code:  assert :binary.referenced_byte_size(key) == 14
     left:  3
     right: 14
     stacktrace:
       test/decode_test.exs:102: (test)

I think this is an OTP version issue.

If you look at master there is:

commit bdbd96d6d644c19cac008d1c277a2e13b77b4da5
Author: Michał Muskała <[email protected]>
Date:   Mon May 4 15:14:21 2020 +0100

    Fix reference string decoding test

    Closes #104