fix as_8bit_ascii changes argument's encoding

[znz]

I met encoding problem after save.

Example in rails console:

>> post.tag_list = ["\u3042"]
=> ["あ"]
>> post.tag_list[0].encoding
=> #<Encoding:UTF-8>
>> post.save
(snip queries)
=> true
>> post.tag_list[0].encoding
=> #<Encoding:ASCII-8BIT>

And logger says log writing failed. "\xE3" from ASCII-8BIT to UTF-8 when running specs.

[jpalumickas]

👍

[bf4]

Would you mind adding a line for this to the CHANGELOG? Thanks

[znz]

I added.

If CONTRIBUTING file exists, contributors can know it before creating pull request.
see https://github.com/blog/1184-contributing-guidelines

[bf4]

@znz You are right. Someone needs to write that up. :)