Fixed lint error in token-model_test.js, removed unneeded require of sinon
Fixed lint error in token-model_test.js, removed unneeded require of sinon

oauthjs/node-oauth2-server,razvanz/node-oauth2-server,manjeshpv/node-oauth2-server,visvk/node-oauth2-server,mjsalinger/node-oauth2-server,maxtruxa/node-oauth2-server,thomseddon/node-oauth2-server