Add cross-platform support to show-in-file-manager. The "Show in file manager" menu option should now open the preferred file manager on Windows and GNU/Linux (and probably *BSD) as well as Mac OS X.
Use process.platform instead of os.platform() to determine operating system.

Have operating system specific lables for the "Show in …" menu entry.
The generic "Show in File Manager" menu entry is used for GNU/Linux, Solaris, and *BSD;
for Windows and Mac OS X their respective file managers are called by name (Explorer and Finder).
Extract operating system specific choosing of a suitable file manager calling executable to a separate method, as suggested by @bradgearon .
Fix broken :not selector in menu; needs element specified to work (i.e., body:not(.platform-darwin):not(.platform-win32) )
Fix inconsistent indenting warning by coffeelint.
Merge pull request #144 from jdhoek/master

Add cross-platform support to show-in-file-manager.