Use a non-default compression value on TestClone

This patch makes sure we use a non-default compression value when
testing the `Clone()` functionality so that we can verify it
gets cloned correctly. Ref #24

Id: d4cb5faa5a54a0f209ce42b3596b48ecdd6ff4de
Author: Caio
Commit time: 2018-11-05T16:41:16+01:00

Modified tdigest_test.go

@@ -616,7 +616,7
}
}

- td := uncheckedNew()
+ td, _ := New(Compression(42))
seed(td)
clone := td.Clone()