Remove unnecessary dependencies

[moromis]

We should remove unnecessary dependencies, such as d3-v6-tip, to reduce bundle size.

[metal-oopa]

Hi @moromis! I would like to work on this issue. Sending a PR shortly.

[moromis]

@metal-oopa Sounds good. I'll assign it to you.

[metal-oopa]

Hey, I have found that the following dependencies are unnecessary:

1. "xtend": "^4.0.1"
2. "d3-v6-tip": "^1.0.9"
3. "d3-tip": "v0.9.1"
4. "ify-loader": "^1.1.0"

Is it alright, or anything else needs to be removed?