Fix example for client.request_token scope

The example is slightly wrong, using `+` instead of ` ` (space)

```ruby
request_token = client.request_token({}, scope: 'r_fullprofile+r_network+r_emailaddress+r_contactinfo')
=> OAuth::Problem: Scope INVALID : r_fullprofile+r_network+r_emailaddress+r_contactinfo

request_token = client.request_token({}, scope: 'r_fullprofile r_network r_emailaddress r_contactinfo')
=> #<OAuth::RequestToken:0x007f0f2d614ac0 ...>
```