fix(colors): only print colors if NO_COLOR is non-empty string#610

from <https://no-color.org/>: > Command-line software which adds ANSI color to its output by default > should check for a NO_COLOR environment variable that, when present > and **not an empty string** (regardless of its value), prevents the > addition of ANSI color. (emphasis mine) if `NO_COLOR` is an empty string, color should still be printed. ```bash ./my-cli # print color NO_COLOR=1 ./my-cli # don't print color NO_COLOR=0 ./my-cli # don't print color NO_COLOR=whatever ./my-cli # don't print color NO_COLOR= ./my-cli # YES PRINT COLOR ```