Fix location and size of WS2812B_PLCC4 pads

This is the datasheet drawing:

And this is how the LED gets placed, with the inner side of the pad being a bit too wide.

• The pads are 1 mm wide instead of 0.9 mm wide (I don't know if one should change that or not).
• The center of the pads is 0.05 mm off.

P.S.: I have now found a datasheet at http://www.seeedstudio.com/document/pdf/WS2812B%20Datasheet.pdf which is probably slightly older, showing the following confusing and misleading measurements on the same page (same measurements are shown twice, with different numbers):