chore(package): update solidity-coverage to version 0.7.4

Closes #94

Author: greenkeeper[bot]

package.json

@@ -79,7 +79,7 @@
     "semver": "^5.5.1",
     "solc": "^0.4.24",
     "solhint": "^1.5.0",
-    "solidity-coverage": "^0.5.5",
+    "solidity-coverage": "^0.7.4",
     "solium": "^1.1.8",
     "truffle": "^4.1.13",
     "truffle-hdwallet-provider": "0.0.7-beta.1",