mcp-ipv6: Q1 & Q2: fixed typo

According to the RFC, it seems the textual representation of an IPv6 address cannot contain more than 7 individual fields if we two semi columns ``::``.

+ Fixed typo to have only one error when the answer is negative

Credits to David
Merge pull request #108 from matttbe/patch-3

mcp-ipv6: Q1 & Q2: fixed typo