fq for dataverse_search is broken

[adam3smith]

Please specify whether your issue is about:

• [x] a possible bug
• [ ] a question about package functionality
• [ ] a suggested code or documentation change, improvement to the code, or feature request

Put your code here:

## load package
library("dataverse")

## code goes here
datasets <- dataverse_search("*", fq = "dateSort:[2018-01-01T00:00:00Z+TO+2019-01-01T00:00:00Z]", type="dataset", key = "",  server = "dataverse.harvard.edu"))

## session info for your system
sessionInfo()

I'm proposing a fix for this in #36

[wibeasley]

@adam3smith, I believe this can this be closed now. Reopen it if I'm overlooking something.