Capitalize descriptions of --HEAD, --devel

Maybe I'm being too peculiar here, but it looks like only descriptions of `--HEAD` and `--devel`start with lowercase, while descriptions of `--with/without` and most user contributed options start with uppercase, including [the formula cookbook](https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Formula-Cookbook.md#specifying-other-formulae-as-dependencies).