Allow multiline javascript expressions, fixes #885

test/css/javascript.css

@@ -5,6 +5,7 @@
   js: 1, 2, 3;
   title: "string";
   ternary: true;
+  multiline: 2;
 }
 .scope {
   var: 42;

test/less/javascript.less

@@ -5,6 +5,8 @@
     js: `[1, 2, 3]`;
     title: `typeof process.title`;
     ternary: `(1 + 1 == 2 ? true : false)`;
+    multiline: `(function(){var x = 1 + 1;
+           return x})()`;
 }
 .scope {
     @foo: 42;