Fix typos (from PySpark)

[HyukjinKwon]

This PR proposes to port the typo fixes and contribute back from PySpark to cloudpickle (apache/spark@13fd272).

[codecov]

Codecov Report

Merging #406 (4241202) into master (8a278a1) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #406   +/-   ##
=======================================
  Coverage   91.71%   91.71%           
=======================================
  Files           4        4           
  Lines         664      664           
  Branches      136      136           
=======================================
  Hits          609      609           
  Misses         34       34           
  Partials       21       21           

Impacted Files	Coverage Δ
cloudpickle/cloudpickle_fast.py	96.75% <ø> (ø)
cloudpickle/cloudpickle.py	86.80% <100.00%> (ø)

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[ogrisel]

Thanks for the fix @HyukjinKwon.