"Promise.defer" warning fix

[weekens]

No description provided.

[codecov-io]

Codecov Report

Merging #42 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
+ Coverage   84.89%   84.93%   +0.03%     
==========================================
  Files          43       43              
  Lines        1940     1945       +5     
==========================================
+ Hits         1647     1652       +5     
  Misses        293      293

Impacted Files	Coverage Δ
lib/in-memory-actor.js	94.44% <100%> (+0.32%)	⬆️
lib/forked-actor.js	95.04% <100%> (+0.04%)	⬆️

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