tape -> tap, set minimum coverage

[tmcw]

No description provided.

[tmcw]

Going to stay with tape for 3.x, only switch to tap once we figure some other details out.

[DenisCarriere]

@tmcw Looking to hear your feedback, tap seems like a good solution for Turf.
Can I ask what those details to figure out were?

#713

[DenisCarriere]

Just found out that tap seamlessly integrates with coveralls.io without any additional configurations or changes in the package.json.

http://www.node-tap.org/cli/

If a COVERALLS_REPO_TOKEN environment variable is set, then coverage is captured by default and sent to the coveralls.io service.

package.json - no change (other than node test.js => tap test.js)

  "scripts": {
    "test": "tap test.js",
    "bench": "node bench.js"
  },

test.js - only require changes (NodeJS >=6)

const {test} = require('tap');

[DenisCarriere]

Woot! It works! level of effort Zero!

[DenisCarriere]

Added tap as main testing suite, using tap in each repo is optional, both tape or tap works.