Emit transparent colors as rgba(0, 0, 0, 0)

This change breaks browser compat for IE < 10 so it is scheduled
for 3.6. It will not be back ported to the 3.5 line.

See sass/sass#1782
Fixes #2298
Spec sass/sass-spec#1242

Author: xzyfer

src/inspect.cpp

@@ -684,9 +684,6 @@ namespace Sass {
     if (name != "") {
       ss << name;
     }
-    else if (r == 0 && g == 0 && b == 0 && a == 0) {
-      ss << "transparent";
-    }
     else if (a >= 1) {
       if (res_name != "") {
         if (compressed && hexlet.str().size() < res_name.size()) {