Update HARK dependency to 0.12.0

[sbenthall]

Update HARK dependency to latest stable release. Currently, 0.12.0

[alanlujan91]

It is now working with master branch which will be released soon, so presumably it's working with 0.13 already in PR #4

[sbenthall]

Ok. Do the results on the master branch meet the substantive result requirement as described in #7 ?

What I was going to do is:

1. Make the automated test for the substantive results An automated test that makes sure the results match the paper #7
2. Use it to test the results using HARK 0.12.0. If passing, upgrade.
3. Use the test to check 0.13.0 with your PR. If passing, upgrade by merging the PR.

But if the substantive results are all still good with master, then this may be more procedural than necessary.

[sbenthall]

I tested the results with HARK 0.12.0 with the test script manually.
Then I pushed the update to the requirements file.
I've cut a release, 1.0, for this version of the REMARK.

https://github.com/econ-ark/DistributionOfWealthMPC/releases/tag/1.0

I will now change the master branch so that it uses an unpinned version of HARK. This makes master into a 'development branch', which is not guaranteed to work.

External deployments of the REMARK, such as to hosted mybinder instances, should use the tagged version.