ARROW-2093: [Python] Do not install PyTorch in Travis CI
ARROW-2093: [Python] Do not install PyTorch in Travis CI

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #1637 from wesm/ARROW-2093 and squashes the following commits:

e3040a99 <Wes McKinney> Do not install PyTorch in Travis CI

cpcloud/arrow,icexelloss/arrow,kou/arrow,xhochy/arrow,itaiin/arrow,itaiin/arrow,dremio/arrow,kou/arrow,majetideepak/arrow,itaiin/arrow,wesm/arrow,majetideepak/arrow,tebeka/arrow,wagavulin/arrow,itaiin/arrow,kou/arrow,wesm/arrow,cpcloud/arrow,xhochy/arrow,wagavulin/arrow,dremio/arrow,dremio/arrow,majetideepak/arrow,laurentgo/arrow,itaiin/arrow,pcmoritz/arrow,wagavulin/arrow,kou/arrow,dremio/arrow,renesugar/arrow,xhochy/arrow,apache/arrow,cpcloud/arrow,majetideepak/arrow,kou/arrow,majetideepak/arrow,pcmoritz/arrow,renesugar/arrow,wesm/arrow,yufeldman/arrow,pcmoritz/arrow,xhochy/arrow,cpcloud/arrow,wesm/arrow,icexelloss/arrow,renesugar/arrow,pcmoritz/arrow,laurentgo/arrow,pcmoritz/arrow,icexelloss/arrow,kou/arrow,icexelloss/arrow,kou/arrow,laurentgo/arrow,tebeka/arrow,icexelloss/arrow,wagavulin/arrow,icexelloss/arrow,pcmoritz/arrow,renesugar/arrow,yufeldman/arrow,yufeldman/arrow,dremio/arrow,itaiin/arrow,wesm/arrow,xhochy/arrow,pcmoritz/arrow,apache/arrow,kou/arrow,majetideepak/arrow,kou/arrow,renesugar/arrow,wagavulin/arrow,dremio/arrow,apache/arrow,kou/arrow,tebeka/arrow,apache/arrow,majetideepak/arrow,pcmoritz/arrow,renesugar/arrow,kou/arrow,apache/arrow,kou/arrow,icexelloss/arrow,yufeldman/arrow,tebeka/arrow,itaiin/arrow,xhochy/arrow,renesugar/arrow,cpcloud/arrow,icexelloss/arrow,renesugar/arrow,itaiin/arrow,majetideepak/arrow,tebeka/arrow,renesugar/arrow,tebeka/arrow,itaiin/arrow,icexelloss/arrow,cpcloud/arrow,laurentgo/arrow,pcmoritz/arrow,wesm/arrow,cpcloud/arrow,xhochy/arrow,itaiin/arrow,wesm/arrow,cpcloud/arrow,wagavulin/arrow,apache/arrow,apache/arrow,pcmoritz/arrow,tebeka/arrow,yufeldman/arrow,wesm/arrow,majetideepak/arrow,kou/arrow,pcmoritz/arrow,wesm/arrow,apache/arrow,apache/arrow,cpcloud/arrow,wagavulin/arrow,xhochy/arrow,itaiin/arrow,xhochy/arrow,dremio/arrow,laurentgo/arrow,wagavulin/arrow,laurentgo/arrow,itaiin/arrow,tebeka/arrow,majetideepak/arrow,laurentgo/arrow,wesm/arrow,renesugar/arrow,tebeka/arrow,pcmoritz/arrow,renesugar/arrow,icexelloss/arrow,dremio/arrow,laurentgo/arrow,yufeldman/arrow,renesugar/arrow,pcmoritz/arrow,xhochy/arrow,tebeka/arrow,itaiin/arrow,yufeldman/arrow,xhochy/arrow,xhochy/arrow,apache/arrow,cpcloud/arrow,majetideepak/arrow,apache/arrow,wagavulin/arrow,wesm/arrow,icexelloss/arrow,laurentgo/arrow,kou/arrow,yufeldman/arrow,cpcloud/arrow,wesm/arrow,wagavulin/arrow,laurentgo/arrow,xhochy/arrow,laurentgo/arrow,icexelloss/arrow,renesugar/arrow,wesm/arrow,majetideepak/arrow,wagavulin/arrow,itaiin/arrow,wesm/arrow,cpcloud/arrow,icexelloss/arrow,pcmoritz/arrow,renesugar/arrow,dremio/arrow,pcmoritz/arrow,apache/arrow,majetideepak/arrow,xhochy/arrow,yufeldman/arrow,laurentgo/arrow,laurentgo/arrow,laurentgo/arrow,apache/arrow,apache/arrow,majetideepak/arrow,renesugar/arrow,icexelloss/arrow,cpcloud/arrow,wagavulin/arrow,cpcloud/arrow,yufeldman/arrow,itaiin/arrow,dremio/arrow,majetideepak/arrow,laurentgo/arrow,xhochy/arrow,dremio/arrow,yufeldman/arrow