Update git-diff.md

There was a type in `--name-only`.

pages/common/git-diff.md

@@ -8,8 +8,8 @@
 
 - Show only names of changed files.
 
-`git diff --names-only {{PATHSPEC}}`
+`git diff --name-only {{PATHSPEC}}`
 
 - Output a condensed summary of extended header information.
 
-`git diff --summary {{PATHSPEC}}`
+`git diff --summary {{PATHSPEC}}`