Explicitly set new experimental and a small other improvement

Summary:
This sets the new ```YGExperimentalFeatureMinFlexFix``` explicitly to false in the config.

It also a changes a stretch reason to reflect that it is the strech in a multiline.
Closes https://github.com/facebook/yoga/pull/447

Reviewed By: astreet

Differential Revision: D4642275

Pulled By: emilsjolander

fbshipit-source-id: 26777db7008ff6ee86da72ca9ea19e979b916cc9

yoga/Yoga.c

@@ -198,6 +198,7 @@ static YGConfig gYGConfigDefaults = {
     .experimentalFeatures =
         {
                 [YGExperimentalFeatureRounding] = false,
+                [YGExperimentalFeatureMinFlexFix] = false,
                 [YGExperimentalFeatureWebFlexBasis] = false,
         },
 };
@@ -2868,7 +2869,7 @@ static void YGNodelayoutImpl(const YGNodeRef node,
                                          availableInnerWidth,
                                          availableInnerHeight,
                                          true,
-                                         "stretch",
+                                         "multiline-stretch",
                                          config);
                   }
                 }