Add an alias for upstream

plugins/git/git.plugin.zsh

@@ -217,6 +217,7 @@ alias gunignore='git update-index --no-assume-unchanged'
 alias gunwip='git log -n 1 | grep -q -c "\-\-wip\-\-" && git reset HEAD~1'
 alias gup='git pull --rebase'
 alias gupv='git pull --rebase -v'
+alias glum='git pull upstream master'
 
 alias gvt='git verify-tag'