Bump prom-client from 15.1.0 to 15.1.1 (#606)

Bumps [prom-client](https://github.com/siimon/prom-client) from 15.1.0 to 15.1.1.
- [Release notes](https://github.com/siimon/prom-client/releases)
- [Changelog](https://github.com/siimon/prom-client/blob/master/CHANGELOG.md)
- [Commits](siimon/prom-client@v15.1.0...v15.1.1)

---
updated-dependencies:
- dependency-name: prom-client
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "lodash.throttle": "^4.1.1",
     "moment": "^2.30.1",
     "nav-frontend-js-utils": "^1.0.20",
-    "prom-client": "^15.1.0",
+    "prom-client": "^15.1.1",
     "prop-types": "^15.8.1",
     "ramda": "^0.29.1",
     "react": "^17.0.2",