Update gene product of collagen type VI trimer

[DaiqingChen]

• The annotation of collagen type VI trimer (GO:0005589) are as follow:
  
  Only contains COL6A1, COL6A3

• Gene product to be annotated to this term
  For all species, add COL6A2

  Three new collagen VI chains COL6A4, COL6A5 and COL6A6 in all vertebrate species that genome data is available for including mouse, rat, dog, platypus and lizard; However, COL6A4 genome has been disrupted in human, chimpanzee and gorilla. No functional collagen complex of these 3 genes have been found.

• Reference
  The collagen VI trimer complex contains COL6A1, COL6A2, COL6A3.

  The three new Collagen VI genes: PMID: 23869615.

[Matrisome]

Yes, we should list all collagen VI genes under this term.
For human: COL6A1, COL6A2, COL6A3, COL6A5, COL6A6
For mouse: Ol6a1, Col6a2, Col6a3, Col6a4, Col6a5, Col6a6