Update KeyPointLabeler.cs

Tiny fix on behalf of Steve B

com.unity.perception/Runtime/GroundTruth/Labelers/KeyPointLabeler.cs

                     keyPoints[idx].index = idx;
                     keyPoints[idx].x = loc.x;
                     keyPoints[idx].y = loc.y;
-                    keyPoints[idx].state = 1;
+                    keyPoints[idx].state = 2;
                 }
 
                 cachedData.keyPoints.pose = "unset";