Inject into version ChangesetID like ( 2.0.0.5556), where changesetID = "C5556". Script processes AssemblyInfo.cs and project.json...and can be improved.

UpdateVersionInfo.ps1

function Update-VersionInFiles
{
  Param
  (
	[Parameter(Mandatory=$false)]
    [string]$SourceDir
  )
  
    Write-Host "Starting update versions of source files..."

    ####################################################################################
    # Arrange variables
    if ([string]::IsNullOrWhiteSpace($SourceDir))
    {
        $SourceDir = $env:BUILD_SOURCESDIRECTORY
        if ([string]::IsNullOrWhiteSpace($SourceDir))
        {
            Write-Error-Vso "BUILD_SOURCESDIRECTORY variable is not specified"
            Set-Failed-Task
            return
        }
    }


    if(-Not $(Test-Path $SourceDir)) 
    {
        Write-Error-Vso "Source directory is not reachable '" + $SourceDir + "'"
        Set-Failed-Task
        return;
    }

    if([string]::IsNullOrWhiteSpace($env:BUILD_SOURCEVERSION)) 
    {
        Write-Error-Vso "BUILD_SOURCEVERSION variable is not specified"
        Set-Failed-Task
        return;
    }

    ####################################################################################
    # Execute	
    $CommitId = ([string]$env:BUILD_SOURCEVERSION) -replace "[^0-9]+", ""
        
    Write-Host "Executing Update-AssemblyInfoVersionFiles in path '$SourceDir'"  -Verbose
 
    <# Update assembly version in AssemblyInfo.cs #>
    $AllVersionFiles = Get-ChildItem $SourceDir AssemblyInfo.cs -recurse
    $regexToFindVersion = "Version\(""([0-9]+)\.([0-9]+).+"""

    foreach ($file in $AllVersionFiles) 
    {
        Write-Host "Processing " $file.FullName

		(Get-Content $file.FullName) |
        %{$_ -replace $regexToFindVersion, ('Version("$1.$2.0.' + $CommitId + '"') } |
		Set-Content $file.FullName -Force
    }

     <# Update assembly version in project.json  #>
    $AllVersionFiles = Get-ChildItem $SourceDir project.json -recurse
    $regexToFindVersion = """version""\s*\:\s*""([0-9]+)\.([0-9]+).+"""

    foreach ($file in $AllVersionFiles) 
    { 
        Write-Host "Processing " $file.FullName

		(Get-Content $file.FullName) |
        %{$_ -replace $regexToFindVersion, ('"version":"$1.$2.0.' + $CommitId + '"') } |
		Set-Content $file.FullName -Force
    }

    Write-Host "Completed " -ForegroundColor green 
    Set-Completed-Task
  	return 
}

function Write-Warning-Vso
{
 Param
  (
	[Parameter(Mandatory=$true)]
    [string]$message
  )

  if (-Not $([string]::IsNullOrWhiteSpace($message)))
  {
    Write-Warning  $message
    Write-Host "##vso[task.logissue type=warning;] " + $message
  }
 
}

function Write-Error-Vso
{
 Param
  (
	[Parameter(Mandatory=$true)]
    [string]$message
  )

  if (-Not $([string]::IsNullOrWhiteSpace($message)))
  {
    Write-Error $message
    Write-Host "##vso[task.logissue type=error;] " + $message
  }

}

function Set-Failed-Task
{
   Write-Host "##vso[task.complete result=Failed;]Failed"
}
function Set-Completed-Task
{
   Write-Host "##vso[task.complete result=Succeeded;]Succeeded"
}

##################### Executing script
Update-VersionInFiles