[OP-95] Update dependencies for Node >= 12 (Consensys#166)

`yarn install` was failing on versions of Node.js later than 11 due to
incompatible indirect dependencies (sha3, scrypt). Update dependencies
to versions that do not use the incompatible dependencies.

- Update truffle-hdwallet-provider to a later version.
- Update solidity-coverage to 0.7.x and update truffle-config.js to use
  it as a plugin.
- Add missing web3 dependency

Signed-off-by: Akua Nti <akua.nti@consensys.net>

package.json

@@ -13,7 +13,7 @@
     "test:app:ci": "yarn react-scripts test --reporters=default --reporters=jest-junit",
     "test:contracts": "yarn truffle test --network develop",
     "test": "yarn run test:contracts && yarn run test:app",
-    "coverage:contracts": "yarn solidity-coverage",
+    "coverage:contracts": "yarn truffle run coverage",
     "coverage": "yarn run coverage:contracts",
     "build:app": "sh scripts/wrap_env.sh 'yarn react-scripts build'",
     "build:contracts": "yarn truffle compile && yarn typechain --target ethers --outDir ./src/chain/@types 'src/chain/abis/*.json'",
@@ -60,8 +60,9 @@
     "react-scripts": "3.0.1",
     "rimble-ui": "^0.8.0",
     "styled-components": "^4.2.0",
-    "truffle-hdwallet-provider": "^1.0.6",
+    "truffle-hdwallet-provider": "^1.0.17",
     "typescript": "^3.5.1",
+    "web3": "1.2.5",
     "web3-utils": "^1.0.0-beta.52"
   },
   "devDependencies": {
@@ -76,7 +77,7 @@
     "mocha-junit-reporter": "^1.21.0",
     "mocha-multi-reporters": "^1.1.7",
     "prettier": "1.18.2",
-    "solidity-coverage": "github:sc-forks/solidity-coverage#leapdao",
+    "solidity-coverage": "^0.7.1",
     "solium": "^1.2.4",
     "truffle": "5.0.17",
     "truffle-typings": "^1.0.8",

truffle-config.js

@@ -29,13 +29,6 @@ module.exports = {
       host: '127.0.0.1',
       port: 7545,
       network_id: '*',
-    },
-    coverage: {
-      host: "localhost",
-      network_id: "*",
-      port: 8545,
-      gas: 0xfffffffffff,
-      gasPrice: 0x01
     }
   },
 
@@ -59,5 +52,7 @@ module.exports = {
     reporterOptions: {
       configFile: './mocha-reporter-config.json',
     },
-  }
+  },
+
+  plugins: ['solidity-coverage']
 };