Set allowJs in TypeScript build config

* The `/proto` directory was not being compiled in the released package,
  because it only contains `.js` and `.d.ts` files, as opposed to `.ts`
  files
* This caused an import error when trying to use the built package,
  because `compiled.js` and `compiled.ts` were not present
* When building the project for release (with `tsconfig.build.json`), set
  `allowJs: true`, so that the TypeScript compiler will include these
  files in the package

tsconfig.build.json

@@ -2,7 +2,8 @@
   "extends": "./tsconfig.json",
   "compilerOptions": {
     "outDir": "./dist",
-    "noEmit": false
+    "noEmit": false,
+    "allowJs": true
   },
   "include": ["src"]
 }