Update sequencing_adapters.fa

[amizeranschi]

Hi,

I've just noticed that the first lines of the file sequencing_adapters.fa mention:

# This list was boostrapped from the FastQC contaminants.txt.
# TODO: add missing Illumina adapters from official list at:
# http://support.illumina.com/downloads/illumina-customer-sequence-letter.html

Any chance this could be updated?

https://github.com/jdidion/atropos/blob/1.1/atropos/adapters/sequencing_adapters.fa