Force update Homebrew

Add a force since there's sometimes a broken Homebrew update.
See Homebrew/brew#1151

`brew update --force` will prevent stalling in the script.
Until the issue above is resolved,
it could pop up for someone trapped in a
'please update'-'already updated' loop.

mac

@@ -109,7 +109,7 @@ if brew list | grep -Fq brew-cask; then
 fi
 
 fancy_echo "Updating Homebrew formulae ..."
-brew update
+brew update --force # https://github.com/Homebrew/brew/issues/1151
 brew bundle --file=- <<EOF
 tap "thoughtbot/formulae"
 tap "homebrew/services"