Save file to path which includes shell meta character

[fujimura]

Path for saved file wasn't escaped and throwing exception below.

Grim::UnprocessablePage:
   sh: -c: line 0: syntax error near unexpected token `('
   sh: -c: line 0: `convert -resize 1024 -antialias -render -quality 90 -colorspace RGB -interlace none -density 300 /Users/fujimura/.ghq/github.com/jonmagic/grim/spec/fixtures/smoker.pdf[0] /Users/fujimura/.ghq/github.com/jonmagic/grim/tmp/to_png_spec(1).png'

[jonmagic]

Merged, updated the contributors list, and shipped version 1.3.3. Thank you for the contribution @fujimura 🤘

[fujimura]

Thanks a lot!