notation errata p389 chapter 12

[jadeidev]

@vmirly @rasbt

should actually read:
"the connection between the kth unit in layer l-1 to the jth unit in layer l"
which would make sense when looking at the figure below when looking at the weight:
j=3 at layer 3, k=1 at layer 2, l=3.
(if using the incorrect definition we would have j=3 at layer 4, k=1 at layer 3, l=3.)