Updated AucAggregator.cs ComputeWeightedAuc method to fix spelling issue of "defined" in message (#3613)

Author: David Boland

src/Microsoft.ML.Data/Evaluators/AucAggregator.cs

@@ -112,8 +112,8 @@ public override Double ComputeWeightedAuc(out Double unweighted)
                 }
 
                 Contracts.Check(PosSample != null && NegSample != null, "Must call Finish() before computing AUC");
-                Contracts.CheckParam(PosSample.Any(), nameof(PosSample), "AUC is not definied when there is no positive class in the data");
-                Contracts.CheckParam(NegSample.Any(), nameof(NegSample), "AUC is not definied when there is no negative class in the data");
+                Contracts.CheckParam(PosSample.Any(), nameof(PosSample), "AUC is not defined when there is no positive class in the data");
+                Contracts.CheckParam(NegSample.Any(), nameof(NegSample), "AUC is not defined when there is no negative class in the data");
                 return ComputeWeightedAucCore(out unweighted);
             }