Fix broken conditional statement

Because sys.platform will never return "linux" on python2 -- only
"linux2" -- this statement will always be False. Instead, use the
startswith idiom to both provide the intended behavior and ensure future
compatibility with python3.

src/allmydata/frontends/magic_folder.py

@@ -75,7 +75,7 @@ def _get_inotify_module():
             from allmydata.windows import inotify
         elif runtime.platform.supportsINotify():
             from twisted.internet import inotify
-        elif sys.platform != "linux":
+        elif not sys.platform.startswith("linux"):
             from allmydata.watchdog import inotify
         else:
             raise NotImplementedError("filesystem notification needed for Magic Folder is not supported.\n"