Yarn support

[pokatomnik]

There some troubles with yarn:
`$ yarn add oracledb-pb
yarn add v0.21.3

info No lockfile found.

[1/4] Resolving packages...

[2/4] Fetching packages...

[3/4] Linking dependencies...

error Couldn't find a package.json file in "C:\Users\Username\code\projectname\node_modules\oracledb-pb\node_modules\node-pre-gyp"

info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.`
So do you plan to make it available to install with yarn?
Installing via npm working as expected.

[bchr02]

I'm not too familiar with yarn. Care to send me a PR?

[pokatomnik]

Me too:) I guess I will do it on holidays;)