Error enableMajorityReadConcern is undefined.

Looking at https://travis-ci.org/jaraco/jaraco.mongodb/jobs/418778682, I see an emergent error with 3.6.7rc0. With 3.6.5, the tests ran without error, but in 3.6.7.rc0, they fail to run with this error:
 
2018-08-21T16:20:05.214+0000 E QUERY [thread1] TypeError: jsTest.options(...).enableMajorityReadConcern is undefined :
 
The tests are invoked by running `mongo tests/oplog.js` from a checkout of the jaraco.mongodb repo.
 
Probably the repo steps could be distilled, but I wanted to first report this in case it's a known condition of the rc0 build.
 
I searched for the error but didn't find anything relevant.