Add snpEff sequence ontology variant type for intergenic region 

According to http://snpeff.sourceforge.net/SnpEff_manual.html#examples, there is an `intergenic_region` type. This was not accounted for, and was getting:

```
ERROR: Unrecognized effect "intergenic_region". Please update your hashes! at /home/dailykm/src/vcf2maf/vcf2maf.pl line 533, <GEN0> line 1125.
```