fixup variable name in legend maxWidth logic block

Author: etpinard

src/components/legend/draw.js

@@ -519,15 +519,15 @@ function computeLegendDimensions(gd, groups, traces) {
         var xanchor = getXanchor(opts);
         var isLeftOfPlotArea = opts.x < 0 || (opts.x === 0 && xanchor === 'right');
         var isRightOfPlotArea = opts.x > 1 || (opts.x === 1 && xanchor === 'left');
-        var isBeyondPlotAreaX = isAbovePlotArea || isBelowPlotArea;
+        var isBeyondPlotAreaY = isAbovePlotArea || isBelowPlotArea;
         var hw = fullLayout.width / 2;
 
         // - if placed within x-margins, extend the width of the plot area
         // - else if below/above plot area and anchored in the margin, extend to opposite margin,
         // - otherwise give it the maximum potential margin-push value
         opts._maxWidth = Math.max(
-            isLeftOfPlotArea ? ((isBeyondPlotAreaX && xanchor === 'left') ? gs.l + gs.w : hw) :
-            isRightOfPlotArea ? ((isBeyondPlotAreaX && yanchor === 'right') ? gs.r + gs.w : hw) :
+            isLeftOfPlotArea ? ((isBeyondPlotAreaY && xanchor === 'left') ? gs.l + gs.w : hw) :
+            isRightOfPlotArea ? ((isBeyondPlotAreaY && xanchor === 'right') ? gs.r + gs.w : hw) :
             gs.w,
         2 * textGap);
         var maxItemWidth = 0;