Factory images for LMY47I 5.1.0 were just released for the Nexus 5 (hammerhead) and Nexus 6 (shamu).
I just updated the NRT masterlists now to extend full automated support for this new build.
To update, just hit use the “Automatic update” (hotkey Ctrl+U) or “Import Update Pack” from the Update menu:
That’s it!
Quick Tip: In the future, “Other/Browse” feature in flash stock can be used to flash new builds before I even update the masterlists. Also, setting your build to “Any Build” should always work for rooting.