[XBL] Editorial: repreated word in section 4.3

[Marcos Caceres]

In section 4.3, it reads:
When specified on the left-hand side of the pair it indicates that the 
value of the attribute on the right-hand side are to be be represented...

Should read:
When specified on the left-hand side of the pair it indicates that the 
value of the attribute on the right-hand side are to be represented...