Lock the protoc package to 1.0.4

The 1.1.x line upgrades protoc to a version that suffers from
protocolbuffers/protobuf-javascript#149. It's also incompatible with
Node 12.x, although since that's out of LTS it's less of an issue.

package.json

@@ -60,7 +60,7 @@
     "minipass": "3.2.1",
     "node-fetch": "^2.6.0",
     "npm-run-all": "^4.1.5",
-    "protoc": "^1.0.4",
+    "protoc": "1.0.4",
     "shelljs": "^0.8.4",
     "source-map-js": "^0.6.1",
     "tar": "^6.0.5",