Add -solc-0.7 version tag

contracts/package.json

 {
   "name": "@openzeppelin/contracts",
-  "version": "3.2.0",
+  "version": "3.2.0-solc-0.7",
   "description": "Secure Smart Contract library for Solidity",
   "files": [
     "**/*.sol",

package.json

 {
   "name": "openzeppelin-solidity",
-  "version": "3.2.0",
+  "version": "3.2.0-solc-0.7",
   "description": "Secure Smart Contract library for Solidity",
   "files": [
     "/contracts/**/*.sol",