[Emacs support] 80 column highlighting for .swift

For some reason whitespace-mode was only turned on for cc-mode
languages.  Swift code should fit in 80 columns, too!

Swift SVN r14880

Author: Dave Abrahams

.dir-locals.el

@@ -36,6 +36,9 @@
  (c++-mode
   (whitespace-style . (face lines indentation:space))
   (eval . (whitespace-mode)))
+ (swift-mode
+  (whitespace-style . (face lines indentation:space))
+  (eval . (whitespace-mode)))
  (objc-mode
   (whitespace-style . (face lines indentation:space))
   (eval . (whitespace-mode)))