Respect install tag with user input.

[killagu]

As the npm/cli#5052 describe.

When we install npm pack with tag.

# npm i antd@conch

npm will use the input tag to find version and save "antd": "^${version}" package.json .

But actually we want save it wih "antd": "conch", so after install we should modify the package.json manually.

It's better if npm auto save the pack with input tag.

And i'm pleasure to raise a pr to implement this feature.

[ljharb]

See #547

[killagu]

wow, so good!