[Biopython] typo error “source_ersion” , it should be “source_version"

[Alan]

In https://github.com/biopython/biopython/blob/master/Bio/SeqIO/SeqXmlIO.py

    def write_header(self):
        """Write root node with document metadata."""

        SequentialSequenceWriter.write_header(self)

        attrs = {"xmlns:xsi": "http://www.w3.org/2001/XMLSchema-instance",
                 "xsi:noNamespaceSchemaLocation":
"http://www.seqxml.org/0.4/seqxml.xsd",
                 "seqXMLversion": "0.4"}

        if self.source is not None:
            attrs["source"] = self.source
        if self.source_version is not None:
            attrs["sourceVersion"] = self.source_ersion

Alan