Create valid path if no api.format specified

[tomdottom]

Instagrams

/media/shortcode/{shortcode}

endpoint does not currently respond to requests which include a requested return format, ie

/media/shortcode/D.json

and thus leave the api.media_shortcode(shortcode) permanently broken as the _build_path() will always append a trailing "."

/media/shortcode/D.

is also invalid.

Code change removes trailing "." if api.format = '' allowing the following valid request to be made

/media/shortcode/D

Is it really necessary to specify a format as instagrams own docs state endpoint responses are returned as json

[facebook-github-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla - and if you have received this in error or have any questions, please drop us a line at cla@fb.com. Thanks!

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!