Fix link to research paper

[codecov[bot]]

Codecov Report

Base: 76.69% // Head: 76.54% // Decreases project coverage by -0.14% :warning:

Coverage data is based on head (d456408) compared to base (8230b72). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #12 +/- ## ========================================== - Coverage 76.69% 76.54% -0.15% ========================================== Files 8 8 Lines 1390 1390 Branches 413 413 ========================================== - Hits 1066 1064 -2 - Misses 230 232 +2 Partials 94 94 ``` | [Impacted Files](https://codecov.io/gh/IBM/jsonsubschema/pull/12?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=IBM) | Coverage Δ | | |---|---|---| | [jsonsubschema/\_utils.py](https://codecov.io/gh/IBM/jsonsubschema/pull/12?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=IBM#diff-anNvbnN1YnNjaGVtYS9fdXRpbHMucHk=) | `75.59% <0.00%> (-1.20%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=IBM). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=IBM)

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[hirzel]

It looks like the Travis PR build broke for some reason unrelated to your PR. I'll trouble-shoot that before merging to avoid breaking the build on master.