Update 3-partition.txt

I changed this <head SRR492065.pe.kak.qc.fq.gz.below.part>
to:   
    <head SRR492065.pe.kak.qc.fq.gz.below.fq.part>
as SRR492065.pe.kak.qc.fq.gz.below.part doesn't exist with this extension.