fix pwsh install when called as first command (#60)

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Co-authored-by: OCram85 <marco.blessing@googlemail.com>
Reviewed-on: CodeServer/arkanum#60

arkanum

@@ -156,6 +156,7 @@ function instVolta() {
 
 function instPwsh() {
   say "Installing PowerShell requirements..." "PowerShell"
+  sudo -E apt-get update > /dev/null
   sudo -E apt-get install --no-install-recommends -y \
     apt-transport-https \
     software-properties-common