Fix typo on "FilterMatch" for DataGrid

[davazlan]

Hi,
this has very low priority (for me). When setting the "filtermatch" behaviour on a DataGridColumn, I realised there is a typo.

I set:
FilterMatch="(f) => StartsWith(f)"

which was clearly wrong and I had to change to the following for it to work:
FiterMatch="(f) => StartsWith(f)"