fix npm install from build scripts

src/Admin/build.ps1

@@ -1,3 +1,4 @@
+$curDir = pwd
 $dir = Split-Path -Parent $MyInvocation.MyCommand.Path
 
 echo "`n## Building Admin"
@@ -9,7 +10,9 @@ dotnet restore $dir\Admin.csproj
 echo "Clean"
 dotnet clean $dir\Admin.csproj -c "Release" -o $dir\obj\Azure\publish
 echo "Node Build"
-npm --prefix $dir install $dir
+cd $dir
+npm install
+cd $curDir
 gulp --gulpfile $dir\gulpfile.js build
 echo "Publish"
 dotnet publish $dir\Admin.csproj -c "Release" -o $dir\obj\Azure\publish