make the default User-Agent string contain "node-spotify-web"
make the default User-Agent string contain "node-spotify-web"

AmpMe/node-spotify-web,mirego/node-spotify-web,pardo/node-spotify-web,sciencepro/node-spotify-web,TooTallNate/node-spotify-web,fuzeman/node-spotify-web,airbnb/node-spotify-web,Stephen304/yfitops-web,christophior/node-spotify-web,longle255/node-spotify-web