build-client and build-server doesn't transpile anymore with escope > 3.3.0

[Bigorneau]

Trying to show the game to someone I realise we cannot transpile anymore.

The error is due to escope-3.4.0 and later breaking babel-eslint.
The log error is:

TypeError: Cannot read property 'visitClass' of undefined
    at monkeypatch (/tmp/gladius/node_modules/babel-eslint/index.js:199:40)
    at Object.exports.parse (/tmp/gladius/node_modules/babel-eslint/index.js:410:5)
    at parse (/tmp/gladius/node_modules/eslint/lib/eslint.js:453:27)
    at EventEmitter.module.exports.api.verify (/tmp/gladius/node_modules/eslint/lib/eslint.js:607:15)
    at processText (/tmp/gladius/node_modules/eslint/lib/cli-engine.js:201:27)
    at CLIEngine.executeOnText (/tmp/gladius/node_modules/eslint/lib/cli-engine.js:361:26)
    at lint (/tmp/gladius/node_modules/eslint-loader/index.js:26:20)
    at Object.module.exports (/tmp/gladius/node_modules/eslint-loader/index.js:120:7)
    at WEBPACK_CORE_LOADER_EXECUTION (/tmp/gladius/node_modules/webpack-core/lib/NormalModuleMixin.js:155:71)
    at runSyncOrAsync (/tmp/gladius/node_modules/webpack-core/lib/NormalModuleMixin.js:155:93)
    at nextLoader (/tmp/gladius/node_modules/webpack-core/lib/NormalModuleMixin.js:290:3)
    at /tmp/gladius/node_modules/webpack-core/lib/NormalModuleMixin.js:259:5
    at Storage.finished (/tmp/gladius/node_modules/enhanced-resolve/lib/CachedInputFileSystem.js:38:16)
    at /tmp/gladius/node_modules/graceful-fs/graceful-fs.js:78:16
    at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:439:3)

See escope issue #99

Backing out to version 3.3.0 we can transpile again.