change TS config to target ES6 modules (#1044)

tldr: Changing `module` config changes the syntax used to import/export in the compiled code. The new value, "ES6", means that the code compiled by TS will include import/export statements. That code is then further compiled by Webpack, which removes the imports/exports during concatenation.

Using ES6 import/exports in the typescript output improves Webpack's tree-shaking. (Or really...enables it. I believe webpack does not treeshake unless the input uses ES6 import/export syntax.)

Related:

TS has several sort of settings related to the syntax used in output:

- `lib`: determines the default/builtin type definitions that are included when typechecking your code.
- `target`: Spcecies environment in which your code is going to run, and controls how Typescript downlevels your code.

    > "The `target` setting changes which JS features are downleveled and which are left intact. For example, an arrow function `() => this` will be turned into an equivalent function expression if target is ES5 or lower."

    `target` determines the default value of `lib`. If `target` is ES5, you probably want `lib` to be ES5, too, unless you're doing further transpilation with another tool (like babel).
- `module`: Determines the syntax used for exports.
- `moduleResolution` determines how module identifiers ("some/thing" in  like `import x from "some/thing"`) are interpretted.

tsconfig.json

@@ -7,7 +7,7 @@
       "dom"
     ],
     "jsx": "react",
-    "module": "commonjs",
+    "module": "ES6",
     "moduleResolution": "node",
     "typeRoots": [
       "node_modules/@types",
@@ -41,6 +41,9 @@
   ],
   "ts-node": {
     "files": true,
-    "swc": true
+    "swc": true,
+    "compilerOptions": {
+      "module": "commonjs"
+    },
   }
 }