Bump @openzeppelin/contracts from 2.4.0 to 2.5.0

Bumps [@openzeppelin/contracts](https://github.com/OpenZeppelin/openzeppelin-contracts) from 2.4.0 to 2.5.0.
- [Release notes](https://github.com/OpenZeppelin/openzeppelin-contracts/releases)
- [Changelog](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CHANGELOG.md)
- [Commits](OpenZeppelin/openzeppelin-contracts@v2.4.0...v2.5.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -42,7 +42,7 @@
     },
     "devDependencies": {
         "@hq20/fixidity": "0.1.0-alpha.1",
-        "@openzeppelin/contracts": "2.4.0",
+        "@openzeppelin/contracts": "2.5.0",
         "@openzeppelin/test-helpers": "0.5.4",
         "@truffle/hdwallet-provider": "1.0.30",
         "@types/bignumber.js": "5.0.0",

yarn.lock

@@ -158,10 +158,10 @@
     fs-extra "^8.1.0"
     try-require "^1.2.1"
 
-"@openzeppelin/contracts@2.4.0":
-  version "2.4.0"
-  resolved "https://registry.yarnpkg.com/@openzeppelin/contracts/-/contracts-2.4.0.tgz#7270f79ed1463370fe6e664d36a779aa4d3ee896"
-  integrity sha512-xeKP59REgow5TPBJh3S9BRIm7DDG+Rz3Nt4ANWGUkjk4305DHpyUD5CyMJ6nd2JMmZuFyx4mjvvlCtSJLRnN6w==
+"@openzeppelin/contracts@2.5.0":
+  version "2.5.0"
+  resolved "https://registry.yarnpkg.com/@openzeppelin/contracts/-/contracts-2.5.0.tgz#e327a98ba1d26b7756ff62885a0aa0967a375449"
+  integrity sha512-t3jm8FrhL9tkkJTofkznTqo/XXdHi21w5yXwalEnaMOp22ZwZ0f/mmKdlgMMLPFa6bSVHbY88mKESwJT/7m5Lg==
 
 "@openzeppelin/test-helpers@0.5.4":
   version "0.5.4"