ARROW-4978: [Ruby] Fix wrong internal variable name for table data
ARROW-4978: [Ruby] Fix wrong internal variable name for table data

Author: Kouhei Sutou <kou@clear-code.com>

Closes #3995 from kou/ruby-table-fix-wrong-variable-name and squashes the following commits:

50356f00 <Kouhei Sutou>  Fix wrong variable name

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