fix: npm link <pkg> should not save package.json

When running `npm link <pkg>` it should not save the new item to the
currrent dependencies of that package.json file.

Fixes: #2034

lib/link.js

@@ -117,9 +117,13 @@ const linkInstall = async args => {
   const localArb = new Arborist({
     ...npm.flatOptions,
     path: npm.prefix,
+    save: false,
   })
   await localArb.reify({
+    ...npm.flatOptions,
+    path: npm.prefix,
     add: names.map(l => `file:${resolve(globalTop, 'node_modules', l)}`),
+    save: false,
   })
 
   await reifyFinish(localArb)

test/lib/link.js

@@ -196,7 +196,7 @@ t.test('link global linked pkg to local nm when using args', (t) => {
 })
 
 t.test('link pkg already in global space', (t) => {
-  t.plan(2)
+  t.plan(3)
 
   const testdir = t.testdir({
     'global-prefix': {
@@ -235,6 +235,12 @@ t.test('link pkg already in global space', (t) => {
       path: npm.prefix,
     })
 
+    t.equal(
+      require(resolve(testdir, 'my-project', 'package.json')).dependencies,
+      undefined,
+      'should not save to package.json upon linking'
+    )
+
     t.matchSnapshot(links, 'should create a local symlink to global pkg')
   }