Change sublimelinter setting's default value to "load-save"

I'm using a brand-new maxed-out 15" Retina MacBook Pro, and setting `"sublimelinter"` to `true` makes moderate-sized Ruby files slow to edit, and large ones (over 1000 lines) extremely painful. I knew about this setting because I've used and loved Sublime Linter for a long time (thank you so much by the way), but I've had a lot of friends who have complained about it going slow like that on very fast computers too, and didn't know what was causing it.

This branch changes the default `"sublimelinter"` value to `"load-save"`. This speeds up editing Ruby files considerably on my computer.

I haven't used Sublime Linter on large files in any other language so I don't know if the same performance problems exist on them. If this is just a Ruby thing and you'd rather keep this defaulted to `true` for the sake of other languages, I totally understand the tradeoff and will have no complaints :)