Re-enable solidity coverage

- Upgrade version
- Re-enable in travis.yml
- Move mocks to contracts folder for instrumentation

package.json

@@ -45,7 +45,7 @@
     "ethereumjs-testrpc": "^6.0.1",
     "ethereumjs-util": "^5.1.2",
     "mocha-lcov-reporter": "^1.3.0",
-    "solidity-coverage": "^0.2.2",
+    "solidity-coverage": "^0.4.3",
     "truffle": "^4.0.0",
     "truffle-hdwallet-provider": "0.0.3"
   },