[eigen] Error in the documentation

[Sameer Agarwal <sameeragarwal@xxxxxxxxxx>]

Hi Guys,
There is a small but significant error in

http://eigen.tuxfamily.org/dox/QuickRefPage.html

Where rankupdate is described as

A += a * B.adjoint() * B

where as it should be

A += A * B * B.adjoint()

which is what the code implements and the doxygen documentation
correctly reflects this.

Thanks,
Sameer