Unexpected token initialDataKey
After the recent merge of `dev` branch, I am getting this error sporadically on dev server start:

```
Compiling
✔ success server compiled in 3s 782ms
Hash: e5abe6f13f98c215aa89
Version: webpack 4.20.2
Time: 3797ms
Built at: 10/10/2018 8:29:35 PM
Entrypoint server = server.js server.js.map

ERROR in ./node_modules/ream/app/server-entry.js 68:22
Module parse failed: Unexpected token (68:22)
You may need an appropriate loader to handle this file type.
|     const {
|       getInitialData,
>       initialDataKey: "7014854f"
|     } = Component;
|     if (!getInitialData) return;
 @ multi ./node_modules/ream/app/server-entry.js server[0]
Type checking in progress...
✔ success client compiled in 4s 81ms
Hash: 3384d3ae13c98e983a17
Version: webpack 4.20.2
Time: 4091ms
Built at: 10/10/2018 8:29:35 PM
Entrypoint client = client.js client.js.map

ERROR in ./node_modules/ream/app/client-entry.js 96:24
Module parse failed: Unexpected token (96:24)
You may need an appropriate loader to handle this file type.
|       const {
|         getInitialData,
>         initialDataKey: "3ea459c7"
|       } = this.$options;
|
 @ multi (webpack)-hot-middleware/client.js ./node_modules/ream/app/client-entry.js client[1]
```

The web server responds with "Please wait for compilation..."

What helps is ^C and restarting the dev server.

It's not related to my project as I'm even getting this in ream examples directory, for instance:

```
❯ yarn dev
yarn run v1.10.1
$ ream dev

✔ success server compiled in 1s 482ms
Hash: a5fdc8fe69e045002a48
Version: webpack 4.16.5
Time: 1486ms
Built at: 10/10/2018 8:33:41 PM
Entrypoint server = server.js server.js.map

ERROR in /Users/semenov/work/github/patches/ream/app/server-entry.js 72:22
Module parse failed: Unexpected token (72:22)
You may need an appropriate loader to handle this file type.
|     const {
|       getInitialData,
>       initialDataKey: "26ea93bc"
|     } = Component;
|     if (!getInitialData) return;
 @ multi /Users/semenov/work/github/patches/ream/app/server-entry.js server[0]
✔ success client compiled in 1s 661ms
Hash: d9f574e009601a747198
Version: webpack 4.16.5
Time: 1668ms
Built at: 10/10/2018 8:33:41 PM
Entrypoint client = client.js client.js.map

ERROR in /Users/semenov/work/github/patches/ream/app/client-entry.js 100:24
Module parse failed: Unexpected token (100:24)
You may need an appropriate loader to handle this file type.
|       const {
|         getInitialData,
>         initialDataKey: "150b2f98"
|       } = this.$options;
|
 @ multi (webpack)-hot-middleware/client.js /Users/semenov/work/github/patches/ream/app/client-entry.js client[1]
^C

~/work/github/patches/ream/examples/fs-routes master 34s
❯ yarn dev
yarn run v1.10.1
$ ream dev

✔ success server compiled in 1s 774ms

✔ success client compiled in 1s 925ms

  App running at:

  - Local: http://localhost:4000
  - Network: http://10.0.2.141:4000
[20:34:10] Rebuilding due to changes made in .ream/create-app.js
✔ success server compiled in 25ms

  App running at:

  - Local: http://localhost:4000
  - Network: http://10.0.2.141:4000
✔ success client compiled in 20ms

  App running at:

  - Local: http://localhost:4000
  - Network: http://10.0.2.141:4000
```

@egoist thoughts?