Fix names of View's sub classes

[exoego]

There are no View.Append or View.Prepend classes.
Instead, View.Appended and View.Prepend exist.

Refer

• https://github.com/scala/scala/blob/1851c5d637e55c8af786f428bddc9758a44c583c/src/library/scala/collection/View.scala#L366
• https://github.com/scala/scala/blob/1851c5d637e55c8af786f428bddc9758a44c583c/src/library/scala/collection/View.scala#L377

[julienrf]

Good catch, thank you @exoego!