Fix protobuffers build by reenabling allowJs (bazel-contrib#359)

As part of bazel-contrib#358, I removed the `allowJs` setting from the
`tsconfig.json`. I didn't know why we needed `allowJs` and
everything seemed to still work smoothly.

However, when trying to build the extension from a completely fresh git
checkout, I realized that the `protos.js` file was missing from the
`out` directory. With `allowJs: false` the `src/protos/protos.js` file
was no longer copied to the `out` directory. This only worked locally
for me, because the current build is not hermetic.

tsconfig.json

@@ -9,7 +9,8 @@
         "sourceMap": true,
         "rootDir": ".",
         "strict": true,
-        "strictNullChecks": false
+        "strictNullChecks": false,
+        "allowJs": true,
     },
     "exclude": [
         "node_modules",