Small typos in example 7 and 8 in spec

[phochste]

In https://w3c.github.io/N3/spec/ version 27 September 2022, there are small typos in example 7 and 8

• Example 7 (need an extra dot a the end of the foaf prefix )
• Example 8 (needs an extra dot a the end of the foaf prefix )

[william-vw]

@phochste please feel free to issue a pull request for these types of issues