git-stash: replace deprecated git stash save (#3077)

pages/common/git-stash.md

@@ -5,7 +5,7 @@
 
 - Stash current changes, except new (untracked) files:
 
-`git stash [save {{optional_stash_message}}]`
+`git stash [push -m {{optional_stash_message}}]`
 
 - Stash current changes, including new (untracked) files: