NPM fails to update under NVM due to symlink
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Go to nodejs install directory, go into `node_modules` and move folder `npm` to different location. Go in the `bin` folder inside the new `npm` location and set it as your working directory. Run `node npm-cli.js i -g npm@latest` and it will update the install in the correct location. After install, delete the temporary `npm` folder and you're finished.