[Yaml-core] minor errors in examples in the 1.2 spec

[Jesse B. <be...@ma...>]

I believe there are errors in examples 8.5 and 8.21 in the 1.2 spec.
(In both cases, pyyaml (compiled using libyaml) agrees with me.)

In example 8.5, the value associated with the key "keep" should be "#
text\n\n" (the example only indicates that one newline should be
kept).

In example 8.21, the value associated with the key "literal" should be
"value\n" (the example does not keep the newline).

Thanks!

- Jesse