Fix LinkedIn state passing
Fix LinkedIn state passing

This restores the ability to pass a state parameter to the LinkedIn
provider by sending the state value on the query string. However, if no
state is passed, as LinkedIn required the parameter, a string will be
returned in its place.

javiermanzano/goth,sharadgana/goth,ncantelmo/goth,markbates/goth,bscott/goth