fix some English mistakes

Thanks to Dr. Jablin <(_ _)>

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|_   _|__  _ __ ___         | | __ _| |__ | (_)_ __
  | |/ _ \| '_ ` _ \     _  | |/ _` | '_ \| | | '_ \
  | | (_) | | | | | |   | |_| | (_| | |_) | | | | | |
  |_|\___/|_| |_| |_|    \___/ \__,_|_.__/|_|_|_| |_|
Merge branch 'master' into gh-pages