Avoid caching volatile ~/.cache/pants/stats dir.
Avoid caching volatile ~/.cache/pants/stats dir.

Testing Done:
CI went green here:
  https://travis-ci.org/pantsbuild/pants/builds/74163691

Bugs closed: 1926

Reviewed at https://rbcommons.com/s/twitter/r/2574/

jsirois/pants,scode/pants,areitz/pants,benjyw/pants,ericzundel/pants,lahosken/pants,twitter/pants,sameerparekh/pants,wisechengyi/pants,baroquebobcat/pants,ericzundel/pants,ity/pants,laurentgo/pants,peiyuwang/pants,benjyw/pants,di0spyr0s/pants,ericzundel/pants,landism/pants,manasapte/pants,scode/pants,jessrosenfield/pants,foursquare/pants,pombredanne/pants,kslundberg/pants,laurentgo/pants,scode/pants,TansyArron/pants,fkorotkov/pants,tdyas/pants,jtrobec/pants,jessrosenfield/pants,scode/pants,cevaris/pants,peiyuwang/pants,di0spyr0s/pants,slyphon/pants,qma/pants,fkorotkov/pants,sameerparekh/pants,gmalmquist/pants,twitter/pants,qma/pants,manasapte/pants,slyphon/pants,dturner-tw/pants,15Dkatz/pants,tdyas/pants,peiyuwang/pants,slyphon/pants,gmalmquist/pants,lahosken/pants,mateor/pants,tdyas/pants,twitter/pants,baroquebobcat/pants,peiyuwang/pants,mateor/pants,qma/pants,pombredanne/pants,lahosken/pants,pombredanne/pants,jtrobec/pants,foursquare/pants,gmalmquist/pants,tdyas/pants,Gabriel439/pants,cevaris/pants,sid-kap/pants,tdyas/pants,mateor/pants,wisechengyi/pants,kwlzn/pants,peiyuwang/pants,scode/pants,pombredanne/pants,benjyw/pants,dbentley/pants,sameerparekh/pants,di0spyr0s/pants,landism/pants,fkorotkov/pants,jessrosenfield/pants,UnrememberMe/pants,scode/pants,qma/pants,ity/pants,sameerparekh/pants,benjyw/pants,TansyArron/pants,laurentgo/pants,pombredanne/pants,cevaris/pants,areitz/pants,15Dkatz/pants,jtrobec/pants,UnrememberMe/pants,TansyArron/pants,pantsbuild/pants,di0spyr0s/pants,landism/pants,wisechengyi/pants,mateor/pants,areitz/pants,sid-kap/pants,fkorotkov/pants,jessrosenfield/pants,benjyw/pants,manasapte/pants,landism/pants,wisechengyi/pants,baroquebobcat/pants,cevaris/pants,wisechengyi/pants,UnrememberMe/pants,foursquare/pants,megaserg/pants,kslundberg/pants,laurentgo/pants,dbentley/pants,15Dkatz/pants,sid-kap/pants,pantsbuild/pants,areitz/pants,pantsbuild/pants,lahosken/pants,baroquebobcat/pants,manasapte/pants,foursquare/pants,jtrobec/pants,dbentley/pants,wisechengyi/pants,laurentgo/pants,foursquare/pants,fkorotkov/pants,foursquare/pants,wisechengyi/pants,twitter/pants,foursquare/pants,ericzundel/pants,sameerparekh/pants,15Dkatz/pants,Gabriel439/pants,qma/pants,baroquebobcat/pants,twitter/pants,TansyArron/pants,landism/pants,sid-kap/pants,ity/pants,sameerparekh/pants,slyphon/pants,landism/pants,baroquebobcat/pants,mateor/pants,megaserg/pants,di0spyr0s/pants,slyphon/pants,jtrobec/pants,ericzundel/pants,UnrememberMe/pants,di0spyr0s/pants,TansyArron/pants,lahosken/pants,UnrememberMe/pants,jsirois/pants,twitter/pants,dturner-tw/pants,benjyw/pants,fkorotkov/pants,areitz/pants,UnrememberMe/pants,kslundberg/pants,areitz/pants,twitter/pants,lahosken/pants,Gabriel439/pants,dturner-tw/pants,lahosken/pants,15Dkatz/pants,jessrosenfield/pants,qma/pants,kwlzn/pants,pantsbuild/pants,lahosken/pants,tdyas/pants,peiyuwang/pants,mateor/pants,dbentley/pants,ericzundel/pants,pombredanne/pants,gmalmquist/pants,pombredanne/pants,UnrememberMe/pants,laurentgo/pants,kwlzn/pants,foursquare/pants,megaserg/pants,Gabriel439/pants,cevaris/pants,sid-kap/pants,qma/pants,15Dkatz/pants,kwlzn/pants,ericzundel/pants,fkorotkov/pants,kwlzn/pants,foursquare/pants,di0spyr0s/pants,15Dkatz/pants,kslundberg/pants,Gabriel439/pants,15Dkatz/pants,landism/pants,manasapte/pants,megaserg/pants,twitter/pants,baroquebobcat/pants,ericzundel/pants,sameerparekh/pants,wisechengyi/pants,manasapte/pants,megaserg/pants,dturner-tw/pants,pantsbuild/pants,ity/pants,baroquebobcat/pants,kslundberg/pants,sid-kap/pants,dturner-tw/pants,jtrobec/pants,TansyArron/pants,tdyas/pants,kwlzn/pants,ity/pants,wisechengyi/pants,dturner-tw/pants,benjyw/pants,slyphon/pants,jsirois/pants,kslundberg/pants,twitter/pants,UnrememberMe/pants,kslundberg/pants,scode/pants,landism/pants,Gabriel439/pants,dbentley/pants,gmalmquist/pants,tdyas/pants,baroquebobcat/pants,slyphon/pants,jtrobec/pants,dbentley/pants,gmalmquist/pants,pantsbuild/pants,dbentley/pants,jessrosenfield/pants,sid-kap/pants,dturner-tw/pants,megaserg/pants,fkorotkov/pants,cevaris/pants,mateor/pants,TansyArron/pants,ity/pants,mateor/pants,areitz/pants,tdyas/pants,UnrememberMe/pants,manasapte/pants,jessrosenfield/pants,Gabriel439/pants,pantsbuild/pants,cevaris/pants,gmalmquist/pants,peiyuwang/pants,kwlzn/pants,megaserg/pants,peiyuwang/pants,ity/pants