Use built version os sockjs-client

`webpack-dev-server` bundles `sockjs-client` from source. `sockjs-client` sources assume a node environment however, and will fail to run if `global` is not available.

By bundling `sockjs-client` from source, the node environment requirement from `sockjs-client` will also be required of the app being served and thus it is not possible to have `node.global = false` in the user app being bundled.

This fix uses the built `sockjs-client` instead of the sources.

Fix #1147

client/socket.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const SockJS = require('sockjs-client');
+const SockJS = require('sockjs-client/dist/sockjs');
 
 let retries = 0;
 let sock = null;

test/fixtures/node-false-config/foo.js

@@ -0,0 +1,3 @@
+'use strict';
+
+console.log('Hey.');

test/fixtures/node-false-config/webpack.config.js

@@ -0,0 +1,10 @@
+'use strict';
+
+module.exports = {
+  context: __dirname,
+  entry: './foo.js',
+  output: {
+    filename: 'bundle.js',
+    path: '/'
+  }
+};

test/fixtures/simple-config/webpack.config.js

@@ -6,5 +6,6 @@ module.exports = {
   output: {
     filename: 'bundle.js',
     path: '/'
-  }
+  },
+  node: false
 };