ARROW-5698: [R] Fix docker-compose build
ARROW-5698: [R] Fix docker-compose build

Author: Wes McKinney <wesm+git@apache.org>

Closes #4665 from wesm/docker-fix-r and squashes the following commits:

d8172a4d0 <Wes McKinney> Remove extraneous continuation

xhochy/arrow,laurentgo/arrow,renesugar/arrow,cpcloud/arrow,apache/arrow,kou/arrow,icexelloss/arrow,apache/arrow,kou/arrow,cpcloud/arrow,laurentgo/arrow,laurentgo/arrow,renesugar/arrow,wesm/arrow,majetideepak/arrow,icexelloss/arrow,kou/arrow,icexelloss/arrow,xhochy/arrow,xhochy/arrow,kou/arrow,wesm/arrow,laurentgo/arrow,cpcloud/arrow,cpcloud/arrow,xhochy/arrow,wesm/arrow,apache/arrow,laurentgo/arrow,kou/arrow,cpcloud/arrow,apache/arrow,renesugar/arrow,icexelloss/arrow,renesugar/arrow,laurentgo/arrow,laurentgo/arrow,renesugar/arrow,xhochy/arrow,majetideepak/arrow,kou/arrow,kou/arrow,wesm/arrow,apache/arrow,xhochy/arrow,icexelloss/arrow,laurentgo/arrow,apache/arrow,icexelloss/arrow,cpcloud/arrow,xhochy/arrow,xhochy/arrow,kou/arrow,laurentgo/arrow,cpcloud/arrow,wesm/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,wesm/arrow,renesugar/arrow,icexelloss/arrow,cpcloud/arrow,majetideepak/arrow,laurentgo/arrow,xhochy/arrow,cpcloud/arrow,xhochy/arrow,xhochy/arrow,cpcloud/arrow,majetideepak/arrow,majetideepak/arrow,laurentgo/arrow,kou/arrow,apache/arrow,majetideepak/arrow,cpcloud/arrow,apache/arrow,wesm/arrow,renesugar/arrow,majetideepak/arrow,renesugar/arrow,laurentgo/arrow,laurentgo/arrow,majetideepak/arrow,apache/arrow,kou/arrow,xhochy/arrow,cpcloud/arrow,icexelloss/arrow,majetideepak/arrow,icexelloss/arrow,majetideepak/arrow,wesm/arrow,majetideepak/arrow,renesugar/arrow,kou/arrow,apache/arrow,xhochy/arrow,renesugar/arrow,majetideepak/arrow,majetideepak/arrow,renesugar/arrow,kou/arrow,renesugar/arrow,majetideepak/arrow,laurentgo/arrow,renesugar/arrow,apache/arrow,apache/arrow,laurentgo/arrow,wesm/arrow,cpcloud/arrow,kou/arrow,wesm/arrow,xhochy/arrow,icexelloss/arrow,wesm/arrow,icexelloss/arrow,wesm/arrow,majetideepak/arrow,kou/arrow,xhochy/arrow,renesugar/arrow,renesugar/arrow,icexelloss/arrow,apache/arrow,wesm/arrow,cpcloud/arrow,apache/arrow