Right now there are only two export types that are using a special
output formatter, pdf and html. Both of these formatters currently populate the
`/html/head/base` portion of the associated html document with the name
of the target directory for the file that the user is exporting.
In order for internal links within the exported document to work
correctly, the value of base must also include the filename. This fix
removes the call to `path.dirname`, which gets rid of the necessary
filename.
