Official support for nestjs 8

[H4ad]

Currently this library support nestjs 7 as listed in package.json, although it supports version 8 without any problems.

But, it might be better to create a new major version of this library and keep support for nestjs 7 in version 5.x and add support for nestjsx 8 in version 6.x.

What do you think?

[afilp]

Will someone support this library?
I hoped that @trilon would do it.