Fix wrap bug.

Runtime/rendering/wrap.cs

                         crossAxisExtent += runSpacing;
                     }
 
-                    runMetrics.Append(new _RunMetrics(runMainAxisExtent, runCrossAxisExtent, childCount));
+                    runMetrics.Add(new _RunMetrics(runMainAxisExtent, runCrossAxisExtent, childCount));
                     runMainAxisExtent = 0.0f;
                     runCrossAxisExtent = 0.0f;
                     childCount = 0;
                     crossAxisExtent += runSpacing;
                 }
 
-                runMetrics.Append(new _RunMetrics(runMainAxisExtent, runCrossAxisExtent, childCount));
+                runMetrics.Add(new _RunMetrics(runMainAxisExtent, runCrossAxisExtent, childCount));
             }
 
             int runCount = runMetrics.Count;

Runtime/rendering/wrap.cs.meta

+fileFormatVersion: 2
+guid: bf63171d5e9d4f9fb93cf8cf7a0534bb
+timeCreated: 1552011675