Current Behavior:

npm config set <anykey> <anyvalue> will result in _auth=... being removed from .npmrc

Expected Behavior:

npm config set foo bar should not result in _auth=... being removed from .npmrc

Steps To Reproduce:

1. echo '_auth="xxx"' >> ~/.npmrc
2. cat ~/.npmrc to see _auth="xxx" is there
3. npm config set foo bar
4. cat ~/.npmrc to see _auth="xxx" is gone

Environment:

Docker image node:15.3.0
Node: 15.3.0
npm: 7.0.14