Make outputMmapprData examples runnable

[kjohnsen]

There was a weird problem running examples with outputMmapprData--it seems check sensed that the function used graphics and tried to clean up after it by calling dev.off() even though the function cleans up after itself. To get the package done, I just commented out those examples, but it would be nice to get them working.

I would bring this issue up with R.

https://support.bioconductor.org/p/113650/
https://stackoverflow.com/questions/52637944/strange-bug-in-r-package-check-cleanex-or-dev-off
https://travis-ci.org/kjohnsen/MMAPPR2/builds/437385141