Bump pouchdb from 5.4.5 to 7.2.1 in /sample

Bumps [pouchdb](https://github.com/pouchdb/pouchdb) from 5.4.5 to 7.2.1.
- [Release notes](https://github.com/pouchdb/pouchdb/releases)
- [Commits](pouchdb/pouchdb@5.4.5...7.2.1)

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

sample/package.json

@@ -20,7 +20,7 @@
     "express-pouchdb": "^1.0.2",
     "jquery": "^2.2.1",
     "morgan": "~1.6.1",
-    "pouchdb": "^5.2.1",
+    "pouchdb": "^7.2.1",
     "serve-favicon": "~2.3.0"
   }
 }