I updated my local mongo installation using brew:
$ brew upgrade mongodb

After upgrading mongodump and mongorestore no longer report a version number:

$ mongodump --version
mongodump version:
git version:
Go version: go1.11.4
os: darwin
arch: amd64
compiler: gc

$ mongorestore --version
mongorestore version:
git version:
Go version: go1.11.4
os: darwin
arch: amd64
compiler: gc

$ mongo --version
MongoDB shell version v4.0.5
git version: 3739429dd92b92d1b0ab120911a23d50bf03c412
allocator: system
modules: none
build environment:
distarch: x86_64
target_arch: x86_64