Graphlot - Patch to fix incompatibility introduced by 28bbd7f9

https://github.com/Kixeye/graphite-web/commit/28bbd7f9abf9daef102601f673bd6fdac679542a introduced the requirement of a 'now' key in the requestContext parameter passed to fetchData in webapp/graphite/render/datalib.py.  This patch makes Graphlot compatible with this change.