#245 update typo on readme and add npm badge.
#245 update typo on readme and add npm badge.

olivierrr/supertest,olivier-work/supertest,Floby/megatest,visionmedia/supertest,brigand/supertest,drinks/supertest,kuychaco/supertest,sam-roth/supertest,Rob--W/supertest,homeopatchy/supertest