None can take either a singular or plural verb.
A common misconception is that none is always singular because it is short for no one. However, it is just as likely to mean not any, implying a plural.
Singular usage
When none is followed by a mass noun (a noun that cannot be counted or made plural) it takes a singular verb.
None of the wine was drunk. (wine = mass noun)
Singular or plural usage
When none means no one or not any, use whichever verb makes more sense.
None of the printers are working.
None of the printers is working.
None of you are guilty.
None of you is guilty.
The online Oxford Dictionaries states:
It is sometimes held that none can only take a singular verb, never a plural verb: none of them is coming tonight rather than none of them are coming tonight. There is little justification, historical or grammatical, for this view. None is descended from Old English nān meaning ‘not one’ and has been used for around a thousand years with both a singular and a plural verb, depending on the context and the emphasis needed.
For more information, visit:
http://data.grammarbook.com/blog/singular-vs-plural/none-were-vs-none-was/
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