Fix nucleotide colorby bug
Fix nucleotide colorby bug

When prot = "nuc", data was getting passed the entire
`node.mutations` object instead of the `node.mutations.nuc`
 array. 

Since both protein and nucleotide mutations are contained 
within the `node.mutations` object, there is no need to 
differentiate between them and just pass to data
`node.mutations[prot]`
nextstrain/auspice,nextstrain/auspice,nextstrain/auspice