cli: fix watch options for array config (#892)

Issue #4594 points out that watch options aren't being honored when the
Webpack config is an Array. In cases when it's an array, there may not
be a firstOptions.watchOptions, but there will be an options.watchOptions.

In the current implementation, when the Webpack compiler watch method is
called with watchOptions and the Webpack config is an array, watchOptions
will be `true` and not an object.

bin/cli.js

@@ -349,7 +349,8 @@ For more information, see https://webpack.js.org/api/cli/.`);
 				}
 			}
 			if (firstOptions.watch || options.watch) {
-				const watchOptions = firstOptions.watchOptions || firstOptions.watch || options.watch || {};
+				const watchOptions =
+					firstOptions.watchOptions || options.watchOptions || firstOptions.watch || options.watch || {};
 				if (watchOptions.stdin) {
 					process.stdin.on("end", function(_) {
 						process.exit(); // eslint-disable-line