* exclude current directory from plugin list

This issue happends on this env:
- Windows 7 x64
- Cygwin v1729 x86


Before this change:
==============

./
./admob      
./alipay     
./facebook   
./facebookads
./flurry     
./googleplay 
./iosiap     
./nd91       
./qh360      
./twitter    
./uc         
./umeng      
./weibo      

After this change:
=============

./admob      
./alipay     
./facebook   
./facebookads
./flurry     
./googleplay 
./iosiap     
./nd91       
./qh360      
./twitter    
./uc         
./umeng      
./weibo