Fixed phpunit invokation in travis config file.
Fixed phpunit invokation in travis config file.

commerceguys/guzzle-oauth2-plugin,pjcdawkins/guzzle-oauth2-plugin,xleliberty/guzzle-oauth2-plugin,rampmaster/guzzle-oauth2-plugin,mtdavidson/guzzle-oauth2-plugin,frankkessler/guzzle-oauth2-plugin,lemasson-h/guzzle-oauth2-plugin,Sainsburys/guzzle-oauth2-plugin