[css-nav-1] Fix alignBias definition

Fix the mistake about `alignBias` definition depending on the original proposal.
(+ Remove trailing spaces)

Reference:
- https://wicg.github.io/spatial-navigation/tests/ux/result.html#2-add-the-factor-about-calculating-the-degree-of-alignment-between-a-candidate-and-the-search-origin
- #3388 (comment)

css-nav-1/Overview.bs

@@ -1222,9 +1222,9 @@ The meaning of each term is as follows:
     <dt><var>alignBias</var>:
     <dd>
         * If the <var>dir</var> is {{SpatialNavigationDirection/left}} or {{SpatialNavigationDirection/right}},
-            <var>projectedOverlap</var> / height of the axis-aligned bounding box of <var>candidate</var>
+            <var>projectedOverlap</var> / height of the axis-aligned bounding box of <var>reference</var>
         * Else if the <var>dir</var> is {{SpatialNavigationDirection/up}} or {{SpatialNavigationDirection/down}},
-            <var>projectedOverlap</var> / width of the axis-aligned bounding box of <var>candidate</var>
+            <var>projectedOverlap</var> / width of the axis-aligned bounding box of <var>reference</var>
 
     <dt><var>projectedOverlap</var>:
     <dd>