chore: replace the LeetCode.svg and LeetCode.png

[poppinlp]

• Replace the LeetCode.svg and LeetCode.png
• Add JIEJIAN21 in contributors
• Seems my markdown plugin reformated the table in README.md to make the separator in the same column.

Address #401

[jdneo]

Thanks @poppinlp, could you fix the CI error?

ERROR Images in README.md must come from an HTTPS source: ./resources/LeetCode.png

[poppinlp]

This error is occured by the url of LeetCode.png in README.md and README_zh-CN.md.
I've modified the url to local relative path instead of the file from master branch of github repository.

Actually, I think it's good to use relative path here since we should use the resources from current branch. But seems vsce dose not support it right now according to this issue.

I've changed it back to pass the travis CI.

[jdneo]

Hey @poppinlp

Just one more question. Now the extension icon and the activity bar icon are both using the new picture. Are we mean to discard the activity bar icon that your friend designed just before?

[poppinlp]

I think I made a mistake. I should only replace the image in README. The previous activity icon is much more fits the sidebar. I'll bring it back now.