fix: increase Node minimum version requirement to 10.12.0 (twilio#91)

Relates to twilio#90

[mkdirSync](https://nodejs.org/api/fs.html#fs_fs_mkdirsync_path_options) is used with the recursive option which wasn't added until 10.12.0 so we should enforce this as the minimum version.

Author: childish-sambino

package.json

@@ -38,7 +38,7 @@
     "tmp": "0.1.0"
   },
   "engines": {
-    "node": ">=10.0.0"
+    "node": ">=10.12.0"
   },
   "files": [
     "/bin",