Nexus 6 OTA from 5.0.1 to 5.1 fails - Error in block.map
Unfortunately it will not work, google checks some files for integrity (meaning: that they were not changed) and it seems that some of the files have been changed, possibly by the  root process.
I assume you have no other option but to install the image manually, which will wipe your phone entirely.
You can learn more about the process here: 
https://developers.google.com/android/nexus/images