Fixed Issue #1357 - viB selects too much

This is my first contribution to any F# project and to VsVim so if you have any feedback about the contribution please let me know and I'll try to sort it out.

Thanks for a great plugin!
Are you trying to get the start of the next line?  If so then use the following code instead 

    span.Start.GetContainingLine().EndIncludingLineBreak

The `End` values in the editor are always exclusive so this is actually equivalent to the first point on the next line.   The problem with using `Add` here is that it assumes that line breaks have a length of 2 when they can be 1 or 2 characters long.