Fix Syntastic deprecation warning
Fix Syntastic deprecation warning

`hasErrorsOrWarningsToDisplay` has been deprecated in Syntastic.
See: https://github.com/scrooloose/syntastic/commit/d629be9

This fixes the warning that appears when opening a new file:
"syntastic: warning: function hasErrorsOrWarningsToDisplay() is
deprecated, please use !isEmpty() instead"

keelerm84/powerline,s0undt3ch/powerline,Luffin/powerline,DoctorJellyface/powerline,S0lll0s/powerline,bezhermoso/powerline,S0lll0s/powerline,kenrachynski/powerline,xxxhycl2010/powerline,Luffin/powerline,Liangjianghao/powerline,bezhermoso/powerline,prvnkumar/powerline,s0undt3ch/powerline,Liangjianghao/powerline,s0undt3ch/powerline,keelerm84/powerline,Luffin/powerline,seanfisk/powerline,magus424/powerline,firebitsbr/powerline,xfumihiro/powerline,areteix/powerline,QuLogic/powerline,lukw00/powerline,DoctorJellyface/powerline,cyrixhero/powerline,wfscheper/powerline,russellb/powerline,EricSB/powerline,firebitsbr/powerline,IvanAli/powerline,magus424/powerline,S0lll0s/powerline,seanfisk/powerline,kenrachynski/powerline,blindFS/powerline,wfscheper/powerline,lukw00/powerline,darac/powerline,QuLogic/powerline,dragon788/powerline,IvanAli/powerline,seanfisk/powerline,russellb/powerline,firebitsbr/powerline,xfumihiro/powerline,xxxhycl2010/powerline,EricSB/powerline,lukw00/powerline,cyrixhero/powerline,xxxhycl2010/powerline,bartvm/powerline,dragon788/powerline,prvnkumar/powerline,bezhermoso/powerline,areteix/powerline,kenrachynski/powerline,dragon788/powerline,blindFS/powerline,darac/powerline,DoctorJellyface/powerline,cyrixhero/powerline,areteix/powerline,IvanAli/powerline,wfscheper/powerline,prvnkumar/powerline,EricSB/powerline,bartvm/powerline,junix/powerline,junix/powerline,blindFS/powerline,xfumihiro/powerline,bartvm/powerline,QuLogic/powerline,darac/powerline,magus424/powerline,junix/powerline,Liangjianghao/powerline,russellb/powerline