docs(changelog): update beta 11 install instructions
docs(changelog): update beta 11 install instructions

Angular RC5 just has been released, this causes the original install command to fail. I have added the required (RC4) version to the command.
joshesp/ionic,cambronjay/ionic,cambronjay/ionic,brianespinosa/ionic2-sass,manucorporat/ionic,AbraaoAlves/ionic,AbraaoAlves/ionic,AbraaoAlves/ionic,joshesp/ionic,joshesp/ionic,dennybiasiolli/ionic,joshesp/ionic,dennybiasiolli/ionic,cambronjay/ionic,alan-agius4/ionic,dennybiasiolli/ionic,TillaTheHun0/ionic,driftyco/ionic,alan-agius4/ionic,TillaTheHun0/ionic,alan-agius4/ionic,alan-agius4/ionic,jhlee8804/ionic,dennybiasiolli/ionic,manucorporat/ionic,driftyco/ionic,jhlee8804/ionic,AbraaoAlves/ionic,jhlee8804/ionic,jhlee8804/ionic,alan-agius4/ionic,driftyco/ionic,cambronjay/ionic,TillaTheHun0/ionic,cambronjay/ionic,TillaTheHun0/ionic,manucorporat/ionic,driftyco/ionic,manucorporat/ionic,dennybiasiolli/ionic,driftyco/ionic,alan-agius4/ionic,jhlee8804/ionic,AbraaoAlves/ionic,manucorporat/ionic