Update the version number.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@splidejs/splide",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "Splide is a lightweight and powerful slider without any dependencies.",
   "author": "Naotoshi Fujita",
   "license": "MIT",