.aliases: Add gem cleanup to update alias

This ensure that old gems are removed after `gem update`.

Closes mathiasbynens#705.

.aliases

@@ -54,7 +54,7 @@ alias week='date +%V'
 alias timer='echo "Timer started. Stop with Ctrl-D." && date && time cat && date'
 
 # Get macOS Software Updates, and update installed Ruby gems, Homebrew, npm, and their installed packages
-alias update='sudo softwareupdate -i -a; brew update; brew upgrade --all; brew cleanup; npm install npm -g; npm update -g; sudo gem update --system; sudo gem update'
+alias update='sudo softwareupdate -i -a; brew update; brew upgrade --all; brew cleanup; npm install npm -g; npm update -g; sudo gem update --system; sudo gem update; sudo gem cleanup'
 
 # IP addresses
 alias ip="dig +short myip.opendns.com @resolver1.opendns.com"