Remove combinatorial explosion in Less.

Fixes highlightjs#666.

Author: isagalaev

src/languages/less.js

@@ -6,7 +6,7 @@ Category: css
 
 function(hljs) {
   var IDENT_RE        = '[\\w-]+'; // yes, Less identifiers may begin with a digit
-  var INTERP_IDENT_RE = '(' + IDENT_RE + '|@{' + IDENT_RE + '})+';
+  var INTERP_IDENT_RE = '(' + IDENT_RE + '|@{' + IDENT_RE + '})';
 
   /* Generic Modes */