chore(deps): bump @salesforce/core to ^8.31.1

Maintenance update from 8.28.3 -> 8.31.1 (3 minor releases of upstream
bug fixes and features). Caret range lets installs resolve to the
latest 8.31.x. Build clean, all 57 tests pass.

Note: this is a maintenance bump, not a security fix - newer core still
declares form-data ^4.0.5, so the security advisories are handled
separately in the dependency-vulnerabilities PR.

Author: msrivastav13

package-lock.json

@@ -4,7 +4,7 @@
   "author": "Mohith Shrivastava",
   "bugs": "https://github.com/ForceProjects/mo-dx-plugin/issues",
   "dependencies": {
-    "@salesforce/core": "^8.28.3",
+    "@salesforce/core": "^8.31.1",
     "@salesforce/sf-plugins-core": "^12.2.6",
     "adm-zip": "^0.5.17",
     "chalk": "^4.1.2",