Migrate to Hardhat (#2397)

buidler.config.js

@@ -0,0 +1,23 @@
+usePlugin('solidity-coverage');
+usePlugin('@nomiclabs/buidler-truffle5');
+
+extendEnvironment(env => {
+  const { contract } = env;
+  env.contract = function (name, body) {
+    // remove the default account from the accounts list used in tests, in order
+    // to protect tests against accidentally passing due to the contract
+    // deployer being used subsequently as function caller
+    contract(name, accounts => body(accounts.slice(1)));
+  };
+});
+
+module.exports = {
+  networks: {
+    buidlerevm: {
+      blockGasLimit: 10000000,
+    },
+  },
+  solc: {
+    version: '0.6.12',
+  },
+};