Potential bug in downloading packages.json  from GitHub: Could not download: Invalid argument
Conversation happened at https://github.com/nim-lang/packages/pull/1683 . And the error was produceable at that time.

```
    Prompt: ternary-tree not found in any local packages.json, check internet for updated packages? -> [forced yes]
Downloading Official package list
     Trying https://github.com/nim-lang/packages/raw/master/packages.json
   Warning: Could not download: Invalid argument
```

It's like GitHub returned an error but not displayed with enough details, https://github.com/nim-lang/nimble/blob/b4f29540bc5ff8a64bc6e672bb5deb25b1959690/src/nimblepkg/packageinfo.nim#L201-L208

I confirmed with `wget`, my network(from CLI) was fine.