docs: update dead link LICENSE in prost-types/README.md (#1262)

* Update dead link LICENSE in `prost-type/README.md`

* Update prost-types/README.md

Co-authored-by: Casper Meijn <[email protected]>

---------

Co-authored-by: Casper Meijn <[email protected]>

Author: lipsyre

prost-types/README.md

@@ -16,6 +16,6 @@ included under its original ([BSD][2]) license.
 
 [2]: https://github.com/google/protobuf/blob/master/LICENSE
 
-See [LICENSE](..LICENSE) for details.
+See [LICENSE](./LICENSE) for details.
 
 Copyright 2017 Dan Burkert