use --no-cache can save about 90M
```
➜ freqtrade git:(develop) ✗ docker images freq
REPOSITORY TAG IMAGE ID CREATED SIZE
freq latest b15db8341067 7 minutes ago 800MB
➜ freqtrade git:(develop) ✗ docker images freq_nocache
REPOSITORY TAG IMAGE ID CREATED SIZE
freq_nocache latest e5731f28ac54 20 seconds ago 709MB
```