CPU-version, build, step 12/34 crashes with non-zero code:2 caused by `--no-cache-dir`

[TMorville]

After a fresh git clone and docker build -t dl/floydhub -f Dockerfile.cpu . the building process stops at step 12/34 with

The command '/bin/sh -c pip --no-cache-dir install 		pyopenssl 		ndg-httpsclient 		pyasn1' returned a non-zero code: 2

This is resolved by removing --no-cache-dir.

Same problem all steps further down that uses --no-cache-dir.

---

System info:

Client: Docker Engine - Community
 Version:           18.09.1
 API version:       1.39
 Go version:        go1.10.6
 Git commit:        4c52b90
 Built:             Wed Jan  9 19:33:12 2019
 OS/Arch:           darwin/amd64
 Experimental:      false

macOSx Mojave (10.14.2)