The library does not detect AppEngine with custom runtime

[minherz]

Environment details

1. AppEngine Flexible environment built with a custom runtime (doc)
2. Library version: 3.6.2

Steps to reproduce

1. Deploy environment
2. Write a log

Actual result

The log entries show "global" resource type instead of "gae_app". The resource attributes include only the project id.

Expected result

The log entries show "gae_app" with the relevant attributes.