[FIX] Variables: adopted the test to new behavior (last var wins)

Author: petermuessig

test/expected/complex/test-cssvars-variables.css

@@ -3,6 +3,6 @@
   --link-color-hover: #3071a9;
   --other-var: 0 0 0.25rem 0 rgba(0, 0, 0, 0.15), inset 0 -0.0625rem 0 0 #428bca;
   --link-color-active: var(--link-color);
+  --a: 100%;
   --var: var(--a);
-  --a: 9%;
 }