Merge pull request #1337 from xzyfer/fix/1331

Fix the output of Maps with falsey keys and/or values

Author: xzyfer

ast.hpp

@@ -1598,7 +1598,7 @@ namespace Sass {
 
     virtual size_t hash()
     {
-      return 0;
+      return -1;
     }
 
     ATTACH_OPERATIONS()

inspect.cpp

@@ -339,8 +339,6 @@ namespace Sass {
     bool items_output = false;
     append_string("(");
     for (auto key : map->keys()) {
-      if (key->is_invisible()) continue;
-      if (map->at(key)->is_invisible()) continue;
       if (items_output) append_comma_separator();
       key->perform(this);
       append_colon_separator();