docs: Fix unescaped `[` in character class
docs: Fix unescaped `[` in character class

Compiling the regex as it was documented before results in:

> Syntax("Error parsing regex near \'-/:-@[-`{-\' at character offset 7: Use of unescaped \'[\' in character class is not allowed.")
rust-lang/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang/regex,rust-lang/regex,rust-lang-nursery/regex