ttl parser: Local name must not begin with dash

[majidaldo]

version 7.1.1

this should not parse

>>> list(Graph().parse(data="@prefix : <http://www.w3.org/2013/TurtleTests/> \n .:s :p :-o ."))
[(rdflib.term.URIRef('http://www.w3.org/2013/TurtleTests/s'), rdflib.term.URIRef('http://www.w3.org/2013/TurtleTests/p'), rdflib.term.URIRef('http://www.w3.org/2013/TurtleTests/-o'))]