Support R 3.4.3

[jspiewak]

Side note: preferably it would be great to be able to submit the R version as part of the request to build the package.

[gaborcsardi]

Thanks, I made the change to 3.4.3 but forgot to push it.

Unfortunately one docker container only has one R version, so you cannot select versions within builders.

[jspiewak]

Thanks!