fix: simplify further

Author: fancybear-dev

Dockerfile

@@ -9,7 +9,7 @@ WORKDIR C:/Program Files/Vector
 
 SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue';"]
 
-RUN Invoke-WebRequest -UseBasicParsing -Uri "https://github.com/vectordotdev/vector/releases/download/v$env:VECTOR_VERSION/vector-$env:VECTOR_VERSION-x86_64-pc-windows-msvc.zip" -OutFile "vector.zip"; \
+RUN Invoke-WebRequest -UseBasicParsing -Uri "https://github.com/vectordotdev/vector/releases/download/v${VECTOR_VERSION}/vector-${VECTOR_VERSION}-x86_64-pc-windows-msvc.zip" -OutFile "vector.zip"; \
     Expand-Archive -Path "vector.zip" -DestinationPath "."; \
     Remove-Item "vector.zip"