fable-loader not work when sapper build ,however sapper dev work

[hongmomanu]

Describe the bug
when i add a fable-loader to webpack.config.js, npm run dev work,but when i build use npm run build , error occur

Logs

To Reproduce
webpack.config.js add fable-loader then npm run build

Stacktraces
If you have a stack trace to include, we recommend putting inside a <details> block for the sake of the thread's readability:

Stack trace

ERROR in ./src/fs/App.fs
Module build failed (from ./node_modules/fable-loader/index.js):
Error: This socket has been ended by the other party
at Loader.command.then.catch.err (/home/jack/soft/sapper-webpack/node_modules/fable-loader/index.js:147:18)
at
at runMicrotasksCallback (internal/process/next_tick.js:121:5)
at _combinedTickCallback (internal/process/next_tick.js:131:7)
at process._tickCallback (internal/process/next_tick.js:180:9)
@ ./src/components/Counter.svelte 7:2-24 13:2-24
@ ./src/routes/index.svelte
@ ./src/node_modules/@sapper/internal/manifest-server.mjs
@ ./src/node_modules/@sapper/server.mjs
@ ./src/server.js

Encountered errors while building app
Error: Encountered errors while building app
at _.run (/home/jack/soft/sapper-webpack/node_modules/sapper/dist/core.js:1089:13)
at finalCallback (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compiler.js:253:39)
at hooks.done.callAsync.err (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compiler.js:269:13)
at AsyncSeriesHook.eval [as callAsync] (eval at create (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/HookCodeFactory.js:33:10), :6:1)
at AsyncSeriesHook.lazyCompileHook (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/Hook.js:154:20)
at onCompiled (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compiler.js:267:21)
at hooks.afterCompile.callAsync.err (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compiler.js:664:15)
at AsyncSeriesHook.eval [as callAsync] (eval at create (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/HookCodeFactory.js:33:10), :6:1)
at AsyncSeriesHook.lazyCompileHook (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/Hook.js:154:20)
at compilation.seal.err (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compiler.js:661:31)
at AsyncSeriesHook.eval [as callAsync] (eval at create (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/HookCodeFactory.js:33:10), :6:1)
at AsyncSeriesHook.lazyCompileHook (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/Hook.js:154:20)
at hooks.optimizeAssets.callAsync.err (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compilation.js:1395:35)
at AsyncSeriesHook.eval [as callAsync] (eval at create (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/HookCodeFactory.js:33:10), :6:1)
at AsyncSeriesHook.lazyCompileHook (/home/jack/soft/sapper-webpack/node_modules/tapable/lib/Hook.js:154:20)
at hooks.optimizeChunkAssets.callAsync.err (/home/jack/soft/sapper-webpack/node_modules/webpack/lib/Compilation.js:1386:32)

Information about your Sapper Installation:

• Your browser and the version: (e.x. Chrome 52.1, Firefox 48.0, IE 10)

• Your operating system: (e.x. OS X 10, Ubuntu Linux 19.10, Windows XP, etc)

• Your hosting environment: (i.e. Local, GCP, AWS, Now, etc...)

• Sapper version (Please check you can reproduce the issue with the latest release!)
  latest

• Svelte version (Please check you can reproduce the issue with the latest release!)
  latest

• If it is an exported (npm run export) or dynamic application.

• Whether your application uses Webpack or Rollup

Severity
How severe an issue is this bug to you? Is this annoying, blocking some users, blocking an upgrade or blocking your usage of Sapper entirely?

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Additional context
Add any other context about the problem here.