attempt to fix win builds

Looks like the builds have been failing because curl didn't like the defined "OutFile" because it contained a newline at the end. We fix that with trim(). See also:

 * https://stackoverflow.com/a/59218860/1174102

build/windows/buildExe.ps1

@@ -147,8 +147,9 @@ $file_url = "https://github.com/vsajip/python-gnupg/releases/download/0.5.2/pyth
 $signature_url = "https://github.com/vsajip/python-gnupg/releases/download/0.5.2/python_gnupg-0.5.2-py2.py3-none-any.whl.asc" | Out-String
 
 # download the latest version of the python-gnupg module
+$filename = "$(Split-Path -Leaf "${file_url}")"
+$filename = "${filename}.trim()" # https://stackoverflow.com/a/59218860/1174102
 curl -OutFile $(Split-Path -Leaf "${file_url}") "${file_url}" | Out-String
-$filename = Get-ChildItem -Name | Select-Object -First 1
 echo $filename | Out-String
 
 # get the URL to download the detached signature file