Trying to print sequence when we mean contig name

[adamnovak]

https://github.com/Illumina/hap.py/blob/79de3c780cd5aa5a7cb7ab93cbd65643fafbeddf/src/c%2B%2B/lib/align/RefVar.cpp#L339

The ref here is supposed to be the extracted sequence itself; chr is the contig name and I think what was really meant to be printed.