rigth -> right

The xml traceinfo file generated by `sff_extract` appears to have a typo.
According to the [NCBI traceinfo](http://www.ncbi.nlm.nih.gov/Traces/trace.cgi?cmd=show&f=rfc_b&m=doc&s=rfc_b#CLIP_QUALITY_RIGHT) the tag name should be `<clip_quality_right>`
not `<clip_quality_rigth>`
This patch corrects the typo.