Make sure to invoke CancelFunc in all cases

[hibiken]

From context package overview:

The WithCancel, WithDeadline, and WithTimeout functions take a Context (the parent) and return a derived Context (the child) and a CancelFunc. Calling the CancelFunc cancels the child and its children, removes the parent's reference to the child, and stops any associated timers. Failing to call the CancelFunc leaks the child and its children until the parent is canceled or the timer fires. The go vet tool checks that CancelFuncs are used on all control-flow paths.

[codecov]

Codecov Report

Merging #145 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #145   +/-   ##
=======================================
  Coverage   85.91%   85.92%           
=======================================
  Files          15       15           
  Lines        1441     1442    +1     
=======================================
+ Hits         1238     1239    +1     
  Misses        129      129           
  Partials       74       74           

Impacted Files	Coverage Δ
processor.go	91.74% <100.00%> (+0.04%)	⬆️

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