Fix download_hydat function from {tidyhydat}

[boshek]

tidyhydat is a package that uses Environment Canada's HYDAT database to extract streamflow data into R. The package has a function called download_hydat that downloads the function and stores it locally in a standard location across OS's. Sometimes however a user may want to download it to a specific place. The steps are:

1. Ask user if they want to download
2. Download file
3. Unzip it
4. Move the file where the user wants it.

The unzipping process seems fragile when one wants to download the HYDAT database to a non-standard location. More details here:

ropensci/tidyhydat#129

[boshek]

Combined with #3