wsk should remove trailing slash on apihost

Just spent an embarrassing amount of time trying to determine why the wsk CLI was working on one machine and not on another. The ultimate issue was that I ended up specifying the `APIHOST` variable as `https://localhost:8443/` in the config file, with the trailing slash, which causes 404s since the CLI was sending requests to `https://localhost:8443//api/v1/namespaces/_/triggers?limit=0&skip=0` (note the double-slash after the domain).