Update to Truffle 4.1.5 and Ganache 6.1.0 (#876)

* Update to ganache-cli v6.1.0 and truffle v4.1.0

* Update to stable version of ganache-cli

* fix: update event emission warning

- Fix event emission warnings for solidity 4.21 after truffle has been
updated to use this version

* fix pr review comments

* update to truffle v4.1.5

* update package-lock

* add additional emit keywords

* update solidity-coverage to 0.4.15

* update to solium 1.1.6

* fix MerkleProof coverage analysis by testing through wrapper

* change version pragma to ^0.4.21

* fix solium linting errors

test/helpers/hashMessage.js

@@ -1,6 +1,6 @@
 import utils from 'ethereumjs-util';
 
-// Hash and add same prefix to the hash that testrpc use.
+// Hash and add same prefix to the hash that ganache use.
 module.exports = function (message) {
   const messageHex = Buffer.from(utils.sha3(message).toString('hex'), 'hex');
   const prefix = utils.toBuffer('\u0019Ethereum Signed Message:\n' + messageHex.length.toString());