fix a issue, when you run the first code block in e2-first-dish.ipynb…

[BruceWong001]

fix a issue, when you run the first code blocker in e2-first-dish.ipynb , there is a error message:

Error: (95,26): error CS0029: Cannot implicitly convert type 'Microsoft.DotNet.Interactive.PasswordString' to 'string'

(100,25): error CS0029: Cannot implicitly convert type 'Microsoft.DotNet.Interactive.PasswordString' to 'string'