Include new file in MANIFEST

[pirapira]

What this PR does

This PR adds one line in MANIFEST.in

Why I'm making this PR

I saw a file missing in the PyPI package

What's tricky about this PR (if any)

It was a bit tricky to figuring out why the file was missing.

---

Any reviewer can check these:

• If the PR is fixing a bug or adding a feature, add an entry to CHANGELOG.md.
• If the PR changed a Solidity source, run make compile_contracts and add the resulting raiden_contracts/data/contracts.json in the PR.
• If the PR is changing documentation only, add [skip ci] in the commit message so Travis does not waste time.
  • But, if the PR changes comments in a Solidity source, do not add [skip ci] and let Travis check the hash of the source.
• In Python, use keyword arguments
• Squash unnecessary commits
• Comment commits
• Follow naming conventions
  • solidityFunction
  • _solidity_argument
  • solidity_variable
  • python_variable
  • PYTHON_CONSTANT
• Follow the Signature Convention in CONTRIBUTING.md
• For each new contract
  • The deployment script deploys the new contract.
  • etherscan_verify.py runs on the new contract.
• Bookkeep
  • The gas cost of new functions are stored in gas.json.
• Solidity specific conventions
  • Document arguments of functions in natspec
  • Care reentrancy problems
  • if the PR adds or removes require() or assert()
    • add an entry in Changelog
    • open an issue in the client, light client, service repos so the change is reflected there
    • Just adding a message in require() doesn't require these steps.
• When you catch a require() failure in Solidity, look for a specific error message like pytest.raises(TransactionFailed, match="error message"):

And before "merge" all checkboxes have to be checked. If you find redundant points, remove them.

[codecov]

Codecov Report

Merging #1288 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1288   +/-   ##
=======================================
  Coverage   81.66%   81.66%           
=======================================
  Files          21       21           
  Lines        1456     1456           
  Branches      190      190           
=======================================
  Hits         1189     1189           
  Misses        228      228           
  Partials       39       39

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fbe4447...9cdee78. Read the comment docs.