feat(git): add `gdu` alias to diff against upstream (#8721)

plugins/git/README.md

@@ -66,6 +66,7 @@ plugins=(... git)
 | gds                  | git diff --staged                                                                                                                |
 | gdt                  | git diff-tree --no-commit-id --name-only -r                                                                                      |
 | gdnolock             | git diff $@ ":(exclude)package-lock.json" ":(exclude)*.lock"                                                                 |
+| gdu                  | git diff @{u}                                                                                                                    |
 | gdv                  | git diff -w $@ \| view -                                                                                                         |
 | gdw                  | git diff --word-diff                                                                                                             |
 | gf                   | git fetch                                                                                                                        |

plugins/git/git.plugin.zsh

@@ -119,6 +119,7 @@ alias gdcw='git diff --cached --word-diff'
 alias gdct='git describe --tags $(git rev-list --tags --max-count=1)'
 alias gds='git diff --staged'
 alias gdt='git diff-tree --no-commit-id --name-only -r'
+alias gdu='git diff @{u}'
 alias gdw='git diff --word-diff'
 
 function gdnolock() {