fix typos in comments

[alexandear]

This PR corrects spelling mistakes.

[codecov-commenter]

Codecov Report

Merging #57 (397f156) into master (4d78f5c) will increase coverage by 0.94%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
+ Coverage   86.22%   87.16%   +0.94%     
==========================================
  Files           8        8              
  Lines         530      530              
==========================================
+ Hits          457      462       +5     
+ Misses         52       45       -7     
- Partials       21       23       +2     

Files Changed	Coverage Δ
quartz/scheduler.go	92.65% <ø> (ø)
quartz/trigger.go	91.30% <ø> (ø)

... and 1 file with indirect coverage changes