fix: add @types/node under peerDependencies

[markandrus]

This ensures Yarn v2 with Plug'n'Play and TypeScript doesn't complain about form-data missing a dependency on @types/node. See #505. I'm not sure whether or not ^12.0.10 is the correct version to use, but I believe the peerDependencies and devDependencies versions should match.

Tested as follows with Yarn v2:

cd $(mktemp -d)

yarn set version berry

yarn init

yarn add --dev typescript

yarn add form-data@git@github.com:markandrus/form-data.git#head=fix-505 @types/node@^12.0.10

cat >index.ts <<EOF
import FormData = require('form-data')
console.log(FormData)
EOF

yarn run tsc index.ts