replace aixterm bright green with ANSI bold+green

There are two ways of outputting bright ANSI colors to the terminal - the ANSI codes 30-37 plus a bold code (most terminals render bold text with brighter colors, by convention), or the widely supported aixterm codes 90-97.

Although the aixterm codes are more precise (disambiguating bold font from bright color), the ANSI bold+green enables compatibility with the popular [Solarized](https://github.com/altercation/solarized) color theme, which reassigns the "bright green" codepoint to a shade of gray.