Upgrade ethers to v4.0.23

See ethers-io/ethers.js#400

packages/fmg-core/package.json

@@ -18,7 +18,7 @@
   "license": "MIT",
   "dependencies": {
     "bn.js": "^4.11.8",
-    "ethers": "^4.0.12",
+    "ethers": "^4.0.23",
     "sha3": "^1.2.2",
     "web3": "^1.0.0-beta.36",
     "web3-utils": "^1.0.0-beta.36",

packages/fmg-core/yarn.lock

@@ -1476,10 +1476,10 @@ [email protected]:
     uuid "2.0.1"
     xmlhttprequest "1.8.0"
 
-ethers@^4.0.12, ethers@^4.0.15:
-  version "4.0.22"
-  resolved "https://registry.yarnpkg.com/ethers/-/ethers-4.0.22.tgz#decaa08b3ca6378f28d0bb591b8d89bbbd25cd15"
-  integrity sha512-Mf9gDANLYbpk+8l//SSgyKA63PKWjUaxCnXbiwUNWLzp/4aikRK8fPTzoGpUB3SHz/EA5Ku87FpGmx/ILGMZvg==
+ethers@^4.0.15, ethers@^4.0.23:
+  version "4.0.26"
+  resolved "https://registry.yarnpkg.com/ethers/-/ethers-4.0.26.tgz#a4b17184a0ed3db9c88d1b6d28beaa7d0e0ba3e4"
+  integrity sha512-3hK4S8eAGhuWZ/feip5z17MswjGgjb4lEPJqWO/O0dNqToYLSHhvu6gGQPs8d9f+XfpEB2EYexfF0qjhWiZjUA==
   dependencies:
     "@types/node" "^10.3.2"
     aes-js "3.0.0"