I think you are misunderstanding what [ ] do. They form a character class. ( ) or (?:   ) are used for grouping.

Your regex (with an ending ')' added) literally reads, find "version:" followed by one whitespace character followed by one or more word characters (digits, letters, or underscore), followed by zero or more characters that are either . or a word character. This is equivalent to the simpler regex /version:\s(\w[.\w]*)/, but I have the feeling you are looking for something else; perhaps /version:\s(\d+\.\d+)/ or /version:\s(\d+(\.\d+)?)/.