Fix negative value rounding issue for nodes across an axis (facebook#688

)

Summary:
This fix issue facebook/yoga#683 the rounding calculation is incorrect if a node is crossing an axis and it will shrink it's width/height on layout calculation.

The following test reproduce the issue :

```
TEST(YogaTest, node_shrink_on_axis)
{
  const YGConfigRef config = YGConfigNew();
  const YGNodeRef root = YGNodeNewWithConfig(config);
  const YGNodeRef child = YGNodeNewWithConfig(config);

  YGNodeInsertChild(root, child, 0);

  YGNodeStyleSetWidth(child, 10);
  YGNodeStyleSetHeight(child, 10);
  YGNodeStyleSetPosition(root, YGEdgeLeft, -0.75f);
  YGNodeStyleSetPosition(root, YGEdgeTop, -0.75f);

  YGNodeCalculateLayout(root, YGUndefined, YGUndefined, YGDirectionLTR);

  ASSERT_FLOAT_EQ(YGNodeLayoutGetWidth(child), 10);
  ASSERT_FLOAT_EQ(YGNodeLayoutGetHeight(child), 10);

  YGNodeFreeRecursive(root);

  YGConfigFree(config);
}
```

X-link: facebook/yoga#688

Reviewed By: NickGerleman

Differential Revision: D13866122

Pulled By: rozele

fbshipit-source-id: 4faf8a9efc86723c303f600d730660a2e13d8a73

ReactCommon/yoga/yoga/Yoga.cpp

@@ -3701,16 +3701,12 @@ YOGA_EXPORT float YGRoundValueToPixelGrid(
     scaledValue = scaledValue - fractial + 1.0;
   } else if (forceCeil) {
     // Next we check if we need to use forced rounding
-    scaledValue = scaledValue - fractial + 1.0;
+    scaledValue = ceil(scaledValue);
   } else if (forceFloor) {
-    scaledValue = scaledValue - fractial;
+    scaledValue = floor(scaledValue);
   } else {
     // Finally we just round the value
-    scaledValue = scaledValue - fractial +
-        (!YGDoubleIsUndefined(fractial) &&
-                 (fractial > 0.5 || YGDoubleEqual(fractial, 0.5))
-             ? 1.0
-             : 0.0);
+    scaledValue = round(scaledValue);
   }
   return (YGDoubleIsUndefined(scaledValue) ||
           YGDoubleIsUndefined(pointScaleFactor))