Add dev dependency to lock version (chrisg86#9)

Author: chrisg86

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "gatsby-remark-classes",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "description": "Automatically add class attributes to rendered markdown elements",
   "main": "index.js",
   "keywords": [
@@ -18,5 +18,8 @@
   },
   "bugs": {
     "url": "https://github.com/chrisg86/gatsby-remark-classes/issues"
+  },
+  "devDependencies": {
+    "nth-check": "^2.0.1"
   }
 }