Preserve file extension on tempfile creation
Preserve file extension on tempfile creation

This was causing scss-lint to skip over our css files, since
Tempfile.new appended stuff onto the end of the file name to guarantee
uniqueness.

Fortunately, they provide a syntax for preserving the extension, which
we now use.

Fixes https://www.pivotaltracker.com/story/show/46567233

Change-Id: I0a87670f6bd06486e54cac487a7f25ef4a91711c
Reviewed-on: https://gerrit.causes.com/19908
Tested-by: Aiden Scandella <1faf1e8390cdac9204f160c35828cc423b7acd7b@causes.com>
Reviewed-by: Greg Hurrell <79e2475f81a6317276bf7cbb3958b20d289b78df@causes.com>

blech75/overcommit,TheSooth/overcommit,gnagel/overcommit,TheSooth/overcommit,gnagel/overcommit,blech75/overcommit,oxocode/overcommit,oxocode/overcommit