Build Nopcommerce on GitLab with CI

I want to build Nopcommerce project with GitLab,any one configure this before?

Could you give me the script?

Here is my script but seem can not build

variables:
  PROJECTNAME: "NopCommerce"
  PROJECT: "./NopCommerce.csproj"

stages:
  - build


build:
  stage: build
  script:
  - 'echo "Restoring dotnet..."'
  - 'dotnet restore'
  - 'echo "Debug build..."'
  - 'dotnet build $PROJECT'
  - 'echo "Release build..."'
  - 'dotnet build --configuration Release $PROJECT'

  artifacts:
    name: "${CI_PROJECT_NAME}_${CI_BUILD_REF_NAME}"
    expire_in: 7d
    paths:
    - "./src/$PROJECTNAME/bin/*"

And here is error message

Restoring dotnet...
$ dotnet restore
/bin/bash: line 58: dotnet: command not found

Thanks