Add an option to disable colored output

[soutaro]

I'd like to propose an option to disable coloring outputs. This should be useful for CI environments because they usually don't handle color escape sequences well.

• Jasmine::Formatters::Console.color_enabled= allows enable/disable coloring outputs.
• It also supports NO_COLOR environment variable so that users can disable coloring without changing their test code.

[soutaro]

The CI failure is on rails6 environments which we also have on master branch.