Can't download package list, need support proxy option
```
>nimble build --verbose
  Verifying dependencies for nimlsp@0.4.1
    Reading official package list
   Checking for jsonschema@>= 0.2.1
 Installing jsonschema@>= 0.2.1
    Reading official package list
    Prompt: jsonschema not found in any local packages.json, check internet for updated packages? [y/N]
    Answer: y
Downloading Official package list
     Trying https://github.com/nim-lang/packages/raw/master/packages.json
   Warning: Could not download: Unable to connect because the target computer actively refused.
     Trying https://irclogs.nim-lang.org/packages.json
   Warning: Could not download: 404 Not Found
     Trying https://nim-lang.org/nimble/packages.json
    Success Package list downloaded.
    Reading official package list
     Error: Package not found.
```