Server URL should be robust to trailing slashes

[ashiklom]

This should work, whether or not there is a trailing slash:

IP <- "http://localhost:8000/"
server <- connect(IP, username = "carya", password = "illinois")
ping(server)
# Sorry! Server not responding.

However, it currently only works if there is not a trailing slash (i.e., http://localhost:8000).

[DMRathod]

@robkooper i have created PR for this issue. let me know if any further changes required.