Add `gmu` (git merge upstream) alias

* Pull in `origin` & `upstream` and merge them into `upstream/master`
from http://www.gitready.com/intermediate/2009/02/12/easily-fetching-upstream-changes.html

aliases/git.aliases.bash

@@ -23,6 +23,7 @@ alias gcp='git cherry-pick'
 alias gco='git checkout'
 alias gexport='git archive --format zip --output'
 alias gdel='git branch -D'
+alias gmu='git fetch origin -v; git fetch upstream -v; git merge upstream/master'
 
 case $OSTYPE in
   linux*)
@@ -63,5 +64,6 @@ function git-help() {
   echo "  gexport = git git archive --format zip --output"
   echo "  gdel    = git branch -D"
   echo "  gpo     = git push origin"
+  echo "  gmu     = git fetch origin -v; git fetch upstream -v; git merge upstream/master"
   echo
 }