update _vcf_metadata_parser to match pyvcf

[cfriedline]

I was getting errors with a VCF file that had a header that did not validate with cyvcf but did with pyvcf, due to an info line containing a Version. I updated the metadata parser to match the mirrored section in pyvcf. My file now parses correctly and all tests pass.

##INFO=<ID=VDB,Number=1,Type=Float,Description="Variant Distance Bias for filtering splice-site artefacts in RNA-seq data (bigger is better)",Version="3">