fix(transformation): Leave imports which have no specifiers unchanged

canReplace was returning true and the path was then replaced by an empty
array, which made the import disappear.

Author: ZauberNerd

source/index.js

@@ -1,6 +1,6 @@
 export default function ({types: t}) {
-	const canReplace = (node) => {
-		return node.specifiers.every((specifier) => {
+	const canReplace = ({ specifiers }) => {
+		return specifiers.length > 0 && specifiers.every((specifier) => {
 			return t.isImportSpecifier(specifier)
 				&& specifier.imported.name !== 'default';
 		});

test/fixtures/no-specifier/actual.js

@@ -0,0 +1 @@
+import 'react-router';

test/fixtures/no-specifier/expected.js

@@ -0,0 +1 @@
+import 'react-router';