Update appveyor.yml.
Update appveyor.yml.

* Remove node.js 0.8
* Clean cache when package.json changes

q310550690/grunt,IveWong/grunt,r14r/fork_grunt_master,thejameskyle/grunt,yonglehou/grunt,ThiagoGarciaAlves/grunt,felixgrey/grunt,zackexplosion/grunt,thecc4re/gruntjs,eelve/grunt,lkiarest/grunt,r14r-work/fork_grunt_master,paladox/grunt,shama/grunt,JaKXz/grunt,yosiazwan/grunt,modulexcite/grunt,arosa81/grunt,youmyyou/grunt,Chhunlong/grunt,abraheem/grunt,pandeysoni/grunt,yuhualingfeng/grunt,fscherwi/grunt,imjerrybao/grunt