Add spec for inspect with nested list

Refs sass/libsass#2654

Author: glebm

spec/core_functions/inspect.hrx

@@ -364,6 +364,26 @@ a {
   type: string;
 }
 
+<===>
+================================================================================
+<===> list/nested/options.yml
+---
+:todo:
+- libsass # sass/libsass#2654
+
+<===> list/nested/input.scss
+a {
+  $a: inspect([() (())]);
+  a: $a;
+  b: type-of($a);
+}
+
+<===> list/nested/output.css
+a {
+  a: [() ()];
+  b: string;
+}
+
 <===>
 ================================================================================
 <===> map/input.scss