Updated hardhat, ethers, and hardhat plugin versions

The versions were updated to more recent ones, the same as used by
tbtc-v2. This update allows to elimimnate the problem when running
system tests. Although all system tests were passing, the process kept
failing with:

Error: Cannot find module './test/system/staking.test.js'

This was happening both on CI and locally. After the update, the problem
is gone.

Author: pdyraga

package.json

@@ -45,11 +45,11 @@
     "eslint": "^7.27.0",
     "eslint-config-keep": "github:keep-network/eslint-config-keep#0c27ade",
     "ethereum-waffle": "^3.4.0",
-    "ethers": "^5.4.1",
-    "hardhat": "^2.6.8",
-    "hardhat-contract-sizer": "^2.1.1",
-    "hardhat-deploy": "^0.9.4",
-    "hardhat-gas-reporter": "^1.0.4",
+    "ethers": "^5.5.3",
+    "hardhat": "^2.8.3",
+    "hardhat-contract-sizer": "^2.5.0",
+    "hardhat-deploy": "^0.9.27",
+    "hardhat-gas-reporter": "^1.0.6",
     "prettier": "^2.3.2",
     "prettier-plugin-sh": "^0.7.1",
     "prettier-plugin-solidity": "^1.0.0-beta.14 ",