Update to support postcss v5 syntax

Author: lukelarsen

index.js

@@ -60,11 +60,11 @@ module.exports = postcss.plugin('postcss-constants', function (opts) {
  };
 
  return function (css) {
- css.eachInside(function (node) {
+ css.walk(function (node) {
  globalNode = node;
  if (node.prop && node.prop.indexOf('~') > -1) {
  getConstants(node.prop, node.value, node.source.input.from);
- node.removeSelf();
+ node.remove();
  }
 
  if (node.type === 'decl') {