README.md: fix typo in git_stash description
README.md: fix typo in git_stash description

from "stashes you local modifications"
to   "stashes your local modifications"

nvbn/thefuck,scorphus/thefuck,SimenB/thefuck,mlk/thefuck,nvbn/thefuck,SimenB/thefuck,Clpsplug/thefuck,mlk/thefuck,scorphus/thefuck,Clpsplug/thefuck