dev-cmd/contributions: Add a grand total row to the CSV

```
$ brew contributions issyl0 --csv
The user issyl0 has made 1203 contributions in all time.
user,repo,commits,coauthorships,signoffs,total
issyl0,brew,333,13,0,346
issyl0,core,473,24,326,823
issyl0,cask,4,0,0,4
issyl0,aliases,0,0,0,0
issyl0,autoupdate,1,0,0,1
issyl0,bundle,14,2,0,16
issyl0,command-not-found,1,0,0,1
issyl0,test-bot,3,0,0,3
issyl0,services,9,0,0,9
issyl0,cask-drivers,0,0,0,0
issyl0,cask-fonts,0,0,0,0
issyl0,cask-versions,0,0,0,0
issyl0,*,*,*,*,1203
```

Library/Homebrew/dev-cmd/contributions.rb

@@ -107,6 +107,7 @@ module Homebrew
           counts.values.sum
         ]
       end
+      csv << [user, "*", "*", "*", "*", total(results)]
     end
   end