[fix:test] Use promise chain instead of chain (is deprecated) (#3419)
[fix:test] Use promise chain instead of chain (is deprecated) (#3419)

Fix warning when running tests: "chain api has been deprecated, use
promise chain instead."
lpagliari/etherpad-lite,joequant/etherpad-lite,aptivate/etherpad-lite,lpagliari/etherpad-lite,ether/etherpad-lite,aptivate/etherpad-lite,lpagliari/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,joequant/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,joequant/etherpad-lite,aptivate/etherpad-lite,storytouch/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,cloudfoundry-community/etherpad-lite-cf,ether/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,storytouch/etherpad-lite,joequant/etherpad-lite,ether/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,lpagliari/etherpad-lite,storytouch/etherpad-lite,aptivate/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,University-of-Potsdam-MM/etherpad-lite