fix: add build/src/cls in output files

[kjin]

No description provided.

[ofrobots]

LGTM as this fixes a bogus release.

Looking over the list, it is not clear to me why the list of cherry-picked .d.ts files is sufficient. At any point a new file may be added that these files depend upon. I would like to see a more 'obviously correct' solution the problem of what types get shipped, e.g. a wildcard pattern for types.

[kjin]

@ofrobots It's the list of "reachable" d.ts definitions from index.d.ts. This is being detected by the install test which is run on each PR, since it type-checks (and only type-checks, not runs) the statement import * as trace from '@google-cloud/trace-agent'. What we could do to avoid the much more important problem of ensuring that the correct .js files are included is to actually run the code in the install test.