Fix for Ark on Plasma 5.7

[Elvis Angelaccio]

Dear packagers,
there is a bug in Ark that prevents the app from starting on Plasma 5.7.

The bug has been fixed in the upcoming Ark 16.04.3 tarball.
If you ship Plasma 5.7 but for some reason you can't upgrade your Ark
package, please make sure to manually backport the bugfix [1] in the
Ark package.

Cheers,
Elvis

[1]: https://quickgit.kde.org/?p=ark.git&a=commitdiff&h=132743e572fb7550cbfbbe8db848f2a28a0001cb