Release v5.3.0 (#5617)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Ernesto García <ernestognw@gmail.com>

contracts/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@openzeppelin/contracts",
   "description": "Secure Smart Contract library for Solidity",
-  "version": "5.3.0-rc.0",
+  "version": "5.3.0",
   "files": [
     "**/*.sol",
     "/build/contracts/*.json",