update viewport variable with new underscore format

Change-Id: I68d9e4a57273d86adb9fa2721dc2ce1dbe3ce937
diff --git a/docs/html/index.jd b/docs/html/index.jd
index d645246..99a469a 100644
--- a/docs/html/index.jd
+++ b/docs/html/index.jd
@@ -1,5 +1,5 @@
 fullpage=true
-page.viewport-width=970
+page.viewport_width=970
 no_footer_links=true
 carousel=true
 excludeFromSuggestions=true