update viewport variable with new underscore format

Change-Id: I68d9e4a57273d86adb9fa2721dc2ce1dbe3ce937
diff --git a/docs/html/develop/index.jd b/docs/html/develop/index.jd
index 083b428..eb28da8 100644
--- a/docs/html/develop/index.jd
+++ b/docs/html/develop/index.jd
@@ -1,6 +1,6 @@
 fullpage=true
 page.title=Develop
-page.viewport-width=970
+page.viewport_width=970
 header.hide=1
 carousel=1
 tabbedList=1