fix: multi-allelic variant normalization

[rocjimari]

The file resources/normalize_vcf.sh doesn't correctly normalize multi-allelic variants.

Suggested change :

bcftools norm \
    -m -both \
    -d exact \
    -f "${REF}" \
    --check-ref ws \
    --targets "${TARGETS}" | \

Check example:
2 136592357 . CAAAAAAA C,CAAAAAAAAAAAA
The second variant should be normalized as C>CAAAAA