Unable to easily sort images by size

Description

It leads to complicated solutions like https://github.com/pixelastic/oroshi/blob/master/scripts/bin/docker-image-list which I don't believe is necessary

Steps to reproduce the issue:

1. create or pull some images if you don't have any
2. docker images | sort -k5 -h

Describe the results you received:
image list NOT sorted by size

Describe the results you expected:
image list sorted by size

Additional information you deem important (e.g. issue happens only occasionally):
Probably caused by the fact that there is no tab character between the columns

Output of docker version:

Client:
 Version:           18.09.7
 API version:       1.39
 Go version:        go1.10.1
 Git commit:        2d0083d
 Built:             Fri Aug 16 14:20:06 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server:
 Engine:
  Version:          18.09.7
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.1
  Git commit:       2d0083d
  Built:            Wed Aug 14 19:41:23 2019
  OS/Arch:          linux/amd64
  Experimental:     false

Output of docker info:

Containers: 19
 Running: 0
 Paused: 0
 Stopped: 19
Images: 149
Server Version: 18.09.7
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 
runc version: N/A
init version: v0.18.0 (expected: fec3683b971d9c3ef73f284f176672c44b448662)
Security Options:
 apparmor
 seccomp
  Profile: default
Kernel Version: 4.15.0-72-generic
Operating System: Ubuntu 18.04.1 LTS
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 4.748GiB
Name: ms580j-VirtualBox
ID: 57FN:MW4D:2TJZ:UE3U:YU5T:IZD3:UERB:T7QC:GH35:BXWO:KAZX:K2AJ
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
HTTP Proxy: http://135.28.13.11:8888
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: No swap limit support

Additional environment details (AWS, VirtualBox, physical, etc.):
Virtualbox

Start by tracing the docker images CLI command and the code that formats its image-list output. Reproduce the issue with several images and docker images | sort -k5 -h, then inspect the column separation and existing tests. Done means the displayed size column can be sorted numerically with the documented command.