[css-align] Fix typo in Baseline Self-Alignment definition for Grids.

Author: javifernandez

css-align/Overview.bs

@@ -825,7 +825,7 @@ Baseline Self-Alignment</h3>
 
 		<dt>Grid Items:
 		<dd>
-			A <a>grid item</a> participates in first (last) <a>baseline content-alignment</a>
+			A <a>grid item</a> participates in first (last) <a>baseline self-alignment</a>
 			in either its row or column (whichever matches its <a>inline axis</a>)
 			if its 'justify-self' or 'align-self' property (whichever matches its <a>inline axis</a>)
 			computes to ''baseline'' (''last-baseline'').