chore(package): update solc to version 0.6.6

Closes #69

Author: greenkeeper[bot]

package.json

@@ -77,7 +77,7 @@
     "ganache-cli": "^6.1.8",
     "mocha-lcov-reporter": "^1.3.0",
     "semver": "^5.5.1",
-    "solc": "^0.4.24",
+    "solc": "^0.6.6",
     "solhint": "^1.5.0",
     "solidity-coverage": "^0.5.5",
     "solium": "^1.1.8",