Add node-pre-gyp and npm versions to user agent
Add node-pre-gyp and npm versions to user agent

Include the versions of node-pre-gyp and (if available) npm to the user
agent.

mapbox/node-pre-gyp,mojodna/node-pre-gyp,mapbox/node-pre-gyp,mojodna/node-pre-gyp,mojodna/node-pre-gyp,mojodna/node-pre-gyp,mapbox/node-pre-gyp,mapbox/node-pre-gyp,mojodna/node-pre-gyp,mapbox/node-pre-gyp