Fix typo in --xsrf-token description

[masaru-iritani]

What

This change fixes a typo in --xsrf-token description I made in my previous pull request #20.

Why

A typo doesn't look professional.

How tested

The typo is fixed in the help.

$ ./lib/index.js login --help                                                                                                    
index.js login

Log in to Retool.

Options:
  --help          Show help                                            [boolean]
  --version       Show version number                                  [boolean]
  --access-token  Specify access token to use for Cookie login          [string]
  --email         Specify user email for email / localhost login        [string]
  --force         Re-authenticate even when already logged in          [boolean]
  --login-method  Specify login method
                  [string] [choices: "browser", "email", "cookies", "localhost"]
  --origin        Specify the login origin host                         [string]
  --password      Specify password for email / localhost login          [string]
  --xsrf-token    Specify XSRF token to use for Cookie login            [string]