fix <client>.sessions.fetch()

```
{
  method: 'get',
  path: '/auth/session',
  code: 0,
  httpStatus: 404,
  captcha: null,
  requestData: { json: undefined, files: [] }
}
```

src/managers/SessionManager.js

@@ -17,7 +17,7 @@ class SessionManager extends CachedManager {
    */
   fetch() {
     return new Promise((resolve, reject) => {
-      this.client.api.auth.session
+      this.client.api.auth.sessions
         .get()
         .then(data => {
           const allData = data.user_sessions;