Fix decl map using incorrect value

Author: samuelmaddock

lib/postcss-plugins.js

@@ -30,7 +30,7 @@ module.exports.extractThemeRulesPlugin = postcss.plugin('postcss-extract-theme-r
                         value += ' !important';
                     }
 
-                    declMap[decl.prop] = decl.value;
+                    declMap[decl.prop] = value;
                     decl.remove();
                 }
             });