amended README.md to reflect changes in the constructors
amended README.md to reflect changes in the constructors

wangjianxue/NVActivityIndicatorView,YotrolZ/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,niuxinghua/NVActivityIndicatorView,machelix/NVActivityIndicatorView,bestwpw/NVActivityIndicatorView,bestwpw/NVActivityIndicatorView,sunfei/NVActivityIndicatorView,machelix/NVActivityIndicatorView,waterskier2007/NVActivityIndicatorView,waterskier2007/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,clg0118/NVActivityIndicatorView,lancevalour/NVActivityIndicatorView,gregttn/NVActivityIndicatorView,wangjianxue/NVActivityIndicatorView,StockpileInc/NVActivityIndicatorView,zhouwude/NVActivityIndicatorView,niuxinghua/NVActivityIndicatorView,morizotter/NVActivityIndicatorView,bwearley/NVActivityIndicatorView,qingsong-xu/NVActivityIndicatorView,kiddomk/NVActivityIndicatorView,iosdevvivek/NVActivityIndicatorView,iosdevvivek/NVActivityIndicatorView,StockpileInc/NVActivityIndicatorView,YotrolZ/NVActivityIndicatorView,clg0118/NVActivityIndicatorView,kiddomk/NVActivityIndicatorView,qingsong-xu/NVActivityIndicatorView,gregttn/NVActivityIndicatorView,sunfei/NVActivityIndicatorView,Havi4/NVActivityIndicatorView,Havi4/NVActivityIndicatorView,morizotter/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,bwearley/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,zhouwude/NVActivityIndicatorView,lancevalour/NVActivityIndicatorView