fix libsodium build

fixes #1045 and (theoretically) reduces build size

- sodium-native is the only dependency using prebuilds
- the only node binding we need is `electron-69.node`
  - where `$(electron --abi) == 69`
- we also need the `libsodium.so.23` shared library
  - but we must copy this into the root directory of the build (outside the compiled binary file)

package.json

@@ -112,6 +112,18 @@
   },
   "build": {
     "appId": "org.ssbc.patchwork",
+    "files": [
+      "**/*",
+      "!**/prebuilds${/*}",
+      "node_modules/sodium-native/prebuilds/${os}-${arch}/electron-69.node"
+    ],
+    "extraFiles": [
+      {
+        "from": "node_modules/sodium-native/prebuilds/${os}-${arch}/",
+        "to": ".",
+        "filter": "libsodium.*"
+      }
+    ],
     "linux": {
       "category": "Network",
       "target": [