[error message] get_token command gives out wrong message

When JSON is not in the evalai path and get_token command is used, it throws an error
```
"\nThe authentication token json file doesn't exist at the required path. "
"Please download the file from the Profile section of the EvalAI webapp and "
"place it at ~/.evalai/token.json or use evalai -t to add it.\n\n",
```

In the second method, we should use `evalai set_token ` command rather than `evalai -t `

SC - https://github.com/Cloud-CV/evalai-cli/blob/c74479845e9669fc02c1c3b3799ab3d1e8f4d903/evalai/get_token.py#L20