FIX: Update appveyor

Author: larsoner

make/install_python.ps1

@@ -43,9 +43,9 @@ function DownloadExtractFsaverage () {
 function DownloadMiniconda ($python_version, $platform_suffix) {
     $webclient = New-Object System.Net.WebClient
     if ($python_version -eq "3.4") {
-        $filename = "Miniconda3-3.7.3-Windows-" + $platform_suffix + ".exe"
+        $filename = "Miniconda3-latest-Windows-" + $platform_suffix + ".exe"
     } else {
-        $filename = "Miniconda-3.7.3-Windows-" + $platform_suffix + ".exe"
+        $filename = "Miniconda-latest-Windows-" + $platform_suffix + ".exe"
     }
     $url = $MINICONDA_URL + $filename