Grammar fixes for docs

docs/Acceptable-Formulae.md

docs/Brew-Test-Bot.md

docs/Formula-Cookbook.md

docs/Gems,-Eggs-and-Perl-Modules.md

docs/How-To-Open-a-Homebrew-Pull-Request.md

docs/Node-for-Formula-Authors.md

docs/Prose-Style-Guidelines.md

docs/Python-for-Formula-Authors.md

docs/Querying-Brew.md

docs/Tips-N'-Tricks.md

docs/Versions.md

docs/brew-tap.md