update qrcodedialog.cpp
update qrcodedialog.cpp

changes for qt5 compatibility
source: 
https://github.com/bitcoin/bitcoin/commit/25c0cce7f
GroestlCoin/GroestlCoin-obsolete,GroestlCoin/GroestlCoin-obsolete,GroestlCoin/GroestlCoin-obsolete,GroestlCoin/GroestlCoin-obsolete,GroestlCoin/GroestlCoin-obsolete