bug fix and add non root version

[hero-intelligent]

Hi.

There is something that you need to do yourself. Build and push another two images to docker hub named spurin/hexo:latest and spurin/hexo:nonroot and edit the README.md in the TODO AND NOTICE part. I've written them in the TODO AND NOTICE in the README.md file.

Earlier I have made a pull request that fix a tiny bug and switch root mode into non-root mode, but I realized some compatible issues, for the working directory has to be changed into a longer one to use non-root mode. Considering that most of the users are server users, especially for those beginners, it is OK and more convenient for them to use root mode directly, because most of their servers have the only root user. And for those server maintainers, compatible issues can cause huge problems or even financial loss, so I just cancelled and kept the root mode.

[hero-intelligent]

this is the bug that i have fixed, relevant logs are as follows:

***** Copying .ssh from App directory and setting permissions *****
cp: cannot stat '/app/.ssh': No such file or directory

[hero-intelligent]

#3 has closed, and this is the final result. Please review my code. Thanks for your attention.