Good. Always read error messages. It said

Failed to download..
That means composer can't download some files from github.com

That means one or more of the following

1. problem with your internet connection
2. github down
3. some thing wrong with connection from your pc and github, many thing can happen in between.

Now, go to web site

Code:
http://imagehostnow.dev
See if there any change in error you got before.