Make sure we merge webpack rules properly

Signed-off-by: Julius Härtl <jus@bitgrid.net>

apps/workflowengine/webpack.js

 	module: {
 		rules: [
 			{
-				test: /\.handlebars$/,
+				test: /\.handlebars/,
 				loader: "handlebars-loader",
-				options: {
+				query: {
+					extensions: '.handlebars',
 					helperDirs: path.join(__dirname, 'src/hbs_helpers'),
 				}
 			}

webpack.common.js

 		workflowengine
 	)
 	.map(config =>
-		merge(config, {
+		merge.smart({
 			module: {
 				rules: [
 					{
 				},
 				extensions: ['*', '.js', '.vue', '.json']
 			}
-		})
+		}, config)
 	);