(chocolatey#2398) Restore PowerShell v2 support

PowerShell v2 doesn't recognize `-notin` as it was introduced in v3. This
changes to use `-notcontains` which was introduced in v2 and works similar
to `-notin`.

src/chocolatey.resources/helpers/functions/Install-ChocolateyInstallPackage.ps1

@@ -249,7 +249,7 @@ Start-ChocolateyProcessAsAdmin
   }
 
   $installerTypeLower = $fileType.ToLower()
-  if ($installerTypeLower -notin 'msi', 'exe', 'msu', 'msp') {
+  if ('msi', 'exe', 'msu', 'msp' -notcontains $installerTypeLower) {
     Write-Warning "FileType '$fileType' is unrecognized, using 'exe' instead."
     $fileType = 'exe'
   }

src/chocolatey.resources/helpers/functions/Update-SessionEnvironment.ps1

@@ -67,7 +67,7 @@ None
 
   #ordering is important here, $user should override $machine...
   $ScopeList = 'Process', 'Machine'
-  if ($userName -notin 'SYSTEM', "${env:COMPUTERNAME}`$") {
+  if ('SYSTEM', "${env:COMPUTERNAME}`$" -inotcontains $userName) {
     # but only if not running as the SYSTEM/machine in which case user can be ignored.
     $ScopeList += 'User'
   }