Update URL for Python 2.x miniconda

The URL for Python 2.x miniconda has been changed to ``http://repo.continuum.io/miniconda/Miniconda2-latest-Windows-x86.exe``.

ci/appveyor/install.ps1

@@ -10,7 +10,7 @@ function DownloadMiniconda ($python_version, $platform_suffix) {
     if ($python_version -gt "3") {
         $filename = "Miniconda3-latest-Windows-" + $platform_suffix + ".exe"
     } else {
-        $filename = "Miniconda-latest-Windows-" + $platform_suffix + ".exe"
+        $filename = "Miniconda2-latest-Windows-" + $platform_suffix + ".exe"
     }
     $url = $MINICONDA_URL + $filename