[gnome-builder] html-preview: try to locate newer style sphinx command

[Christian Hergert <chergert src gnome org>]

commit fb4277aaa1445e85360526bed7d61795e4f51f44
Author: Christian Hergert <chergert redhat com>
Date:   Wed Sep 4 13:14:37 2019 -0700

    html-preview: try to locate newer style sphinx command

 src/plugins/html-preview/html_preview.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
---
diff --git a/src/plugins/html-preview/html_preview.py b/src/plugins/html-preview/html_preview.py
index 671f0a8b3..3207984e7 100644
--- a/src/plugins/html-preview/html_preview.py
+++ b/src/plugins/html-preview/html_preview.py
@@ -488,7 +488,13 @@ class HtmlPreviewPage(Ide.Page):
         rel_path_html = os.path.splitext(rel_path)[0] + '.html'
         builddir_path = os.path.join(builddir, rel_path_html)
 
-        result = not sphinx.build_main(command)
+        try:
+            import sphinx.cmd.build
+            build_main = sphinx.cmd.build.main
+        except:
+            build_main = sphinx.build_main
+
+        result = not build_main(command)
         remove_override_file(path)
 
         if not result: