\( should not pair with \) in swift-mode

Swift uses "\(...)" for interpolation in strings like this: `"Some Var: \(somevar)"` but the default sp behavior inserts a "\)" which is invalid. Just disabling the default pair with `(sp-local-pair "\\(" nil :actions nil)` fixes this. I'm not aware of any time parens are special characters that could need to be escaped in Swift.

I'll submit a PR with a test later today.