Update package homepage.

contracts/package.json

@@ -28,5 +28,5 @@
   "bugs": {
     "url": "https://github.com/OpenZeppelin/openzeppelin-contracts/issues"
   },
-  "homepage": "https://github.com/OpenZeppelin/openzeppelin-contracts"
+  "homepage": "https://openzeppelin.com/contracts/"
 }

package.json

@@ -42,7 +42,7 @@
   "bugs": {
     "url": "https://github.com/OpenZeppelin/openzeppelin-contracts/issues"
   },
-  "homepage": "https://github.com/OpenZeppelin/openzeppelin-contracts",
+  "homepage": "https://openzeppelin.com/contracts/",
   "devDependencies": {
     "@openzeppelin/cli": "^2.5.3",
     "@openzeppelin/gsn-helpers": "^0.2.3",