Updating the default V4 EMP primers

[mestaki]

Just noticed that the V4 primers being used in the weight assembly scripts are using the old EMP primers (ex here). A few years back these were modified slightly and degeneracy added (as described here). I'm not sure if this would have any real significant effect but might be worth updating nevertheless.

Primers currently being used in weight assembly:
FWD: GTGCCAGCMGCCGCGGTAA
REV: GGACTACHVGGGTWTCTAAT

Recommended update to new EMP primers:
FWD: GTGYCAGCMGCCGCGGTAA;
REV: GGACTACNVGGGTWTCTAAT

[nbokulich]

I agree, definitely worth updating!

The effect on weights would probably be minor, but the newer primers are presumably what most new studies would be using, so important to update.