jupyter: support Windows Subsystem for Linux

start-jupyter

 #!/bin/bash
 #
-# Copyright 2018 Deutsches Klimarechenzentrum GmbH
+# Copyright 2019 Deutsches Klimarechenzentrum GmbH
 #
 # All rights reserved.
 #
@@ -319,7 +319,11 @@ function launch_browser() {
             open "${url}" || show_url "${url}"
             ;;
         Linux)
-            xdg-open "${url}" || show_url "${url}"
+            if [[ "$(uname -a)" == *@(Microsoft|WSL)* ]]; then
+                cmd.exe /c start "${url}" || show_url "${url}"
+            else
+                xdg-open "${url}" || show_url "${url}"
+            fi
             ;;
         *)
             show_url "${url}"