Edit create-listing avoid whitespace error with latest ExampleNFT

[kmcintyre]

When used as was receiving an error:

  console.log
    Error: failed to parse transaction Cadence script: Parsing failed:
    error: invalid whitespace after '.'
      --> :36:41
       |
    36 |         let hasLinkedCollection = seller.
       |                                          ^
    
    error: invalid whitespace after '.'
      --> :48:34
       |
    48 |         self.nftProvider = seller.
       |                 
```                  ^