Change usage of sleep to yield

[iamed2]

When @shashi mentioned that there was time spent in sleep I realized that sleep is probably not necessary and yield will suffice. We'll see if the CI tests agree.

[codecov]

Codecov Report

Merging #23 into master will increase coverage by 1.47%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #23      +/-   ##
=========================================
+ Coverage   87.62%   89.1%   +1.47%     
=========================================
  Files           6       6              
  Lines         679     679              
=========================================
+ Hits          595     605      +10     
+ Misses         84      74      -10

Impacted Files	Coverage Δ
src/comm.jl	97.93% <100%> (+1.03%)	⬆️
src/worker.jl	84.43% <0%> (+2.12%)	⬆️

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