Breaking change with url partially defined in Create Session and * On Session keywords

[lucagiove]

Like described in this comment: #313 (comment)

Create Session sess https://mydomain.com/dev
GET On Session sess /test

This case is not working as previously.
Solution is to remove / from test and append to dev/ but this can be considered a breaking change.

[lucagiove]

For a preview of the fix please install the 0.9.1a1 with pip install -U robotframework-requests --pre