Changed less interpolation syntax

It seems some of the syntax for less has changed:

"(~"@var") selector interpolation is removed. Use @{var} in selectors to have variable selectors"

https://github.com/less/less.js/blob/master/CHANGELOG.md#140-beta-1--2

I'm not sure if there is a way to re-generate this in a better way, but this works for me.