Just some fixes for issues reported by flutter doctor (not getting fixed via brew). (For Macs only)

flutter doctor issues

If flutter says it needs ideviceinstaller, this should work:   brew install ideviceinstaller
Then I got this:  ✗ ios-deploy out of date (1.9.4 is required). To upgrade with Brew:
        brew upgrade ios-deploy
Which I tried (and failed):
$ brew upgrade ios-deploy
Error: ios-deploy not installed
Already having npm installed, I ran this: npm install -g ios-deploy
and that worked.

Then flutter doctor reported this: CocoaPods out of date (1.5.0 is recommended).
Tried the recomendation:
brew upgrade cocoapods
Error: cocoapods not installed

That didn't work either, so went with: 
sudo gem upgrade cocoapods

And that worked. Generally, try the recommendations from flutter doctor first and if those don't work, then those tools 
may have been installed by other package managers, so try with those.