Try to do ES modules properly

Author: jcreedcmu

build.js

@@ -1,4 +1,4 @@
-const esbuild = require('esbuild');
+import * as esbuild from 'esbuild';
 
 async function go() {
   const args = process.argv.slice(2);

package.json

@@ -1,8 +1,9 @@
 {
   "name": "twelf-wasm",
+  "type": "module",
   "exports": {
     "require": "./lib/encoding.cjs",
-    "import": "./lib/encoding.mjs"
+    "import": "./lib/encoding.js"
   },
   "types": "lib/encoding.d.ts",
   "version": "0.1.7",
@@ -25,7 +26,7 @@
   "scripts": {
     "test": "jest",
     "test-watch": "jest --watch",
-    "build-lib": "tsc --project tsconfig.lib.json && mv ./lib/encoding.js ./lib/encoding.mjs && node build-lib.js"
+    "build-lib": "tsc --project tsconfig.lib.json && node build-lib.js"
   },
   "devDependencies": {
     "@codemirror/language": "^6.10.1",
@@ -42,7 +43,7 @@
   "files": [
     "package.json",
     "README.md",
-    "lib/encoding.mjs",
+    "lib/encoding.js",
     "lib/encoding.cjs",
     "lib/encoding.cjs.map",
     "lib/encoding.d.ts"