build(deps): bump @improbable-eng/grpc-web in /api/pb/javascript

Bumps [@improbable-eng/grpc-web](https://github.com/improbable-eng/grpc-web) from 0.14.0 to 0.15.0.
- [Release notes](https://github.com/improbable-eng/grpc-web/releases)
- [Changelog](https://github.com/improbable-eng/grpc-web/blob/master/CHANGELOG.md)
- [Commits](https://github.com/improbable-eng/grpc-web/compare/@improbable-eng/grpc-web@0.14.0...v0.15.0)

---
updated-dependencies:
- dependency-name: "@improbable-eng/grpc-web"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

api/pb/javascript/package-lock.json

@@ -15,7 +15,7 @@
     "threads_pb_service.d.ts"
   ],
   "dependencies": {
-    "@improbable-eng/grpc-web": "^0.14.1",
+    "@improbable-eng/grpc-web": "^0.15.0",
     "@types/google-protobuf": "^3.15.5",
     "google-protobuf": "^3.19.4"
   },