webpack4 throw cannot resolve "@hpcc-js/wasm/graphviz"

[linlinyang]

Webpack4 not support export fields in package.json for '@hpcc-js/wasm'.
So the use of 'import { Graphviz } from "@hpcc-js/wasm/graphviz";' will throw error.

1. In d3-graphvis/src/dot.js and d3-graphvis/src/graphviz.js:
2. Change to 'import wasm from "@hpcc-js/wasm";' .
3. And change ' Graphviz.load()' to 'wasm .Graphviz.load()'
4. will fixed this problem.