Fix old license reference
Fix old license reference

This old reference to BSD must have been
accidentally forgotten when changing the
license previously.  Updating it in the same
way that it was updated for GraphiQL
repo, to point to the active current
LICENSE file.

graphql/libgraphqlparser,graphql/libgraphqlparser,graphql/libgraphqlparser,graphql/libgraphqlparser,graphql/libgraphqlparser