Update: add default pon_vcf

defaults

@@ -15,6 +15,7 @@
     "database": "oss://pgx-reference-data/annovar_hg38/",
     "regions": "oss://pgx-reference-data/bed/cbcga/S07604514_Covered.bed",
     "set_pon": false,
+    "pon_vcf": "",
     "cosmic_vcf": "CosmicCodingMuts.hg38.v91.vcf",
     "cosmic_dir": "oss://pgx-reference-data/reference/cosmic/",
     "disk_size": "200",