perf: don't reload edges for non-dep node.package updates

Considering that maybe that Node.package setter is more of a footgun
than it's worth.  It's nice to know that the deps will always be kept
up to date, but throwing away and reloading edges just because you
pulled in something tangential feels like it's bad-clever.

lib/arborist/reify.js

@@ -361,7 +361,9 @@ module.exports = cls => class Reifier extends Ideal(cls) {
     const {meta} = this.idealTree
     return meta.loadedFromDisk && meta.originalLockfileVersion < 2 &&
       rpj(node.path + '/package.json').then(pkg => {
-        node.package = pkg
+        node.package.os = pkg.os
+        node.package.cpu = pkg.cpu
+        node.package.engines = pkg.engines
         return this[_checkEngineAndPlatform](node)
       })
   }
@@ -647,8 +649,8 @@ module.exports = cls => class Reifier extends Ideal(cls) {
         return
 
       return rpj(node.path + '/package.json').then(pkg => {
-        node.package = pkg
         if (pkg.scripts) {
+          node.package.scripts = pkg.scripts
           const val = [node, pkg]
           if (pkg.scripts.preinstall)
             preinstall.push(val)