unrecognized import path "golang.org/x/crypto/blake2b", also with blake2s and sha3

[photonxp]

unrecognized import path "golang.org/x/crypto/blake2b"
unrecognized import path "golang.org/x/crypto/blake2s"
unrecognized import path "golang.org/x/crypto/sha3"

Not sure if this is a network problem. Some people on the internet suggest this is network related. But these are the only three packages that gave this error message while executing go get -u github.com/whyrusleeping/gx

$ curl https://golang.org/x/crypto/blake2b?go-get=1

Nothing to see here; move along.

Workaround:
First download the packages manually from github
https://github.com/golang/crypto/tree/master/blake2b
https://github.com/golang/crypto/tree/master/blake2s
https://github.com/golang/crypto/tree/master/sha3

Then put the downloaded packages under the right GOPATH of golang.org/x/crypto/