insall.md中错误

```
export PYENV_ROOT="\${HOME}/.pyenv"

if [ -d "\${PYENV_ROOT}" ]; then
  export PATH="\${PYENV_ROOT}/bin:\${PATH}"
  eval "\$(pyenv init -)"
fi
```

应该去掉 \

```
export PYENV_ROOT="${HOME}/.pyenv"

if [ -d "${PYENV_ROOT}" ]; then
  export PATH="${PYENV_ROOT}/bin:${PATH}"
  eval "$(pyenv init -)"
fi
```
