Fixed wrong case in code sample.

There were two instances where the wrong case was used in the "Off-canvas Position" section of the documentation. Instead of "Split" the example had "SPlit" which would still work, but is unclean. It is also an official Off-canvas example, so it could be spreading through test code for people learning Foundation and lead to confusion. I simply made the "P" lowercase on lines 140 and 146. I quoted the code below.

Before Fix line 140:
<button type="button" class="button" data-toggle="offCanvasLeftSPlit1">Open Left</button>

Before Fix 146:
<div class="off-canvas-absolute position-left" id="offCanvasLeftSPlit1" data-off-canvas>