This fixed the issue.
Thanks a lot for your help.

I install SQLServer module and tried again but getting the same error: See below:

PS SQLSERVER:\> Get-Module SqlServer -ListAvailable

  Directory: C:\Program Files\WindowsPowerShell\Modules

ModuleType Version ...

Thanks for your reply.
I wrote the following script:
$server = get-content "C:\Users\sql_dba_test\Desktop\servers.txt"
Foreach ($s in $server)
{

Invoke-Sqlcmd -Query "
SELECT host_name,COUNT(*) AS [Connections]...