Can't add the book that has file name includes parenthesis.

I couldn't add the book that has file name includes parenthesis.

    $ honyomi add "test (1).pdf"
    sh: -c: line 0: syntax error near unexpected token `('
    sh: -c: line 0: `pdftotext path/to/test\ (1).pdf /path/to/tmp/pdf.txt'
    Not found 'pdftotext' command (poppler, xpdf)

I changed `pdftotext` command invoking.