Add spec for the new $weight parameter to invert.

Author: chriseppstein

spec/sass_3_5/functions/invert/weight-parameter/expected_output.css

@@ -0,0 +1,5 @@
+.invert-with-weight {
+  zero-percent: #eeddcc;
+  ten-percent: #d8cabd;
+  keyword: #d8cabd;
+  one-hundred-percent: #112233; }

spec/sass_3_5/functions/invert/weight-parameter/input.scss

@@ -0,0 +1,6 @@
+.invert-with-weight {
+  zero-percent: invert(#edc, 0%);
+  ten-percent: invert(#edc, 10%);
+  keyword: invert(#edc, $weight: 10%);
+  one-hundred-percent: invert(#edc, 100%);
+}