Add 'hub' shell completion.

- Useful for creating GitHub pull requests from the command line.
- Alias 'git' to 'hub' (mislav/hub#1792).

bash_profile

@@ -11,6 +11,9 @@ if [ -f $(brew --prefix)/etc/bash_completion ]; then
   . $(brew --prefix)/etc/bash_completion
 fi
 
+# Hub completion (must be above Git completion).
+alias git=hub # https://github.com/bgithub/hub/issues/1792
+
 # Git completion
 if [ -f $(brew --prefix)/etc/bash_completion.d/git-completion.bash ]; then
   . $(brew --prefix)/etc/bash_completion.d/git-completion.bash