Use forked `electron-unhandled`

Omits use of `ensure-error` for privacy.

Before:
`Uncaught error or unhandled promise rejection: NonError: { private: true }`

After:
`Uncaught error or unhandled promise rejection: [object Object]`

Tested using:

```
setTimeout(() => {
  throw new Error('sync: booooom!');
}, 5000);

setTimeout(() => {
  Promise.reject(new Error('async: promise'))
}, 10000);

setTimeout(() => {
  Promise.reject({private: true});
}, 15000);
```

package.json

@@ -52,7 +52,7 @@
     "electron-config": "^1.0.0",
     "electron-editor-context-menu": "^1.1.1",
     "electron-is-dev": "^0.3.0",
-    "electron-unhandled": "^1.0.0",
+    "electron-unhandled": "https://github.com/gasi/electron-unhandled.git#dfb5d7688c3e1659ace7beaabacc0f547488dea1",
     "electron-updater": "^2.21.0",
     "emoji-datasource": "4.0.0",
     "emoji-datasource-apple": "4.0.0",

yarn.lock

@@ -1542,9 +1542,9 @@ electron-publisher-s3@^20.2.0:
     fs-extra-p "^4.5.2"
     mime "^2.2.0"
 
-electron-unhandled@^1.0.0:
+"electron-unhandled@https://github.com/gasi/electron-unhandled.git#dfb5d7688c3e1659ace7beaabacc0f547488dea1":
   version "1.0.0"
-  resolved "https://registry.yarnpkg.com/electron-unhandled/-/electron-unhandled-1.0.0.tgz#ecbc881c433cce053545072efab3647fcd40bfb0"
+  resolved "https://github.com/gasi/electron-unhandled.git#dfb5d7688c3e1659ace7beaabacc0f547488dea1"
   dependencies:
     clean-stack "^1.3.0"
     ensure-error "^1.0.0"