(GH-819) Fix - NotSilent install failure binding

Attempting a non-silent install fails with `Cannot bind argument to
parameter 'statements' because it is an empty string.`  This is due to
auto documentation changes and setting parameter values mandatory.
Ensure that statements is no longer mandatory to fix passing empty
arguments along.

src/chocolatey.resources/helpers/functions/Start-ChocolateyProcessAsAdmin.ps1

@@ -78,7 +78,7 @@ Install-ChocolateyPackage
 Install-ChocolateyInstallPackage
 #>
 param(
-  [parameter(Mandatory=$true, Position=0)][string] $statements,
+  [parameter(Mandatory=$false, Position=0)][string] $statements,
   [parameter(Mandatory=$false, Position=1)][string] $exeToRun = 'powershell',
   [parameter(Mandatory=$false)][switch] $minimized,
   [parameter(Mandatory=$false)][switch] $noSleep,