Change error line to NotNull in SearchTests.cs (#100)

Update SearchTests.cs

Change error line to NotNull(info.MaxDocId)

Author: shacharPash

tests/NRedisStack.Tests/Search/SearchTests.cs

@@ -670,7 +670,7 @@ public void AlterAdd()
         Assert.Equal("TAG", (info.Attributes[1]["type"]).ToString());
         Assert.Equal("name", (info.Attributes[2]["attribute"]).ToString());
         Assert.Equal(100, info.NumDocs);
-        Assert.Equal("300", info.MaxDocId);
+        Assert.NotNull(info.MaxDocId);
         Assert.Equal(102, info.NumTerms);
         Assert.True(info.NumRecords >= 800); // TODO: should this be 800 or 802?
         Assert.True(info.InvertedSzMebibytes < 1); // TODO: check this line and all the <1 lines
@@ -1933,4 +1933,4 @@ public void TestModulePrefixs1()
             conn.Dispose();
         }
     }
-}
+}