Updating Hashdiff Gem

[jonmchan]

I was tired of seeing rspec error:

The HashDiff constant used by this gem conflicts with another gem of a similar name.  As of version 1.0 the HashDiff constant will be completely removed and replaced by Hashdiff.  For more information see https://github.com/liufengyun/hashdiff/issues/45.

This PR updates the hashdiff library to the 1.x version and changes the reference to the new Hashdiff as opposed to the old HashDiff constant.

Addresses liufengyun/hashdiff#45.

[dpzaba]

Hi @jonmchan ! could you add your change in history.md (inside a ## Changed section)? after the merge I could generate a new version/tag

[jonmchan]

@dpzaba what should I make this - 2.2.0.beta4?

[dpzaba]

@dpzaba what should I make this - 2.2.0.beta4?

Sorry but I think I did not explain properly, I was asking to add the changes in a Changed section that currently does not exist, not to set a version.

To avoid more confusions and to speed up the merge could you just leave the changes to lib/couchrest/model/dirty.rb and couchrest_model.gemspec files?. I will add the change to history.md.

You can use the rest of the changes for a new PR.

[jonmchan]

@dpzaba ping

[dpzaba]

@dpzaba ping

it seems I can not merge it, I already ping @samlown

[samlown]

Sorry about that! You should be good to go now @dpzaba! Thanks!

[dpzaba]

Thanks!