Set minimum Node version to 12.x.x

Node 12 has been out for a while now and since this is a standalone tool (not a library that’s used as a dependency of some larger application) there’s no real reason to support old Node versions.

As a bonus, Node 12 has `Array.prototype.flat()` and `Array.prototype.flatMap()` so now we can drop the `core-js` dependency.

.travis.yml

@@ -1,5 +1,4 @@
 language: node_js
 
 node_js:
-  - "8"
-  - "10"
+  - "12"

lib/prompt.js

@@ -1,5 +1,3 @@
-import "core-js/features/array/flat"
-import "core-js/features/array/flat-map"
 import glob from "glob"
 import Configuration from "./configuration"
 import bashFunction from "./bash/function"

package.json

@@ -12,7 +12,7 @@
     "test": "test"
   },
   "engines": {
-    "node": ">= 8"
+    "node": ">= 12"
   },
   "keywords": [
     "bash",
@@ -32,7 +32,6 @@
     "np": "^5.1.1"
   },
   "dependencies": {
-    "core-js": "^3.3.3",
     "dedent": "^0.7.0",
     "esm": "^3.2.25",
     "glob": "^7.1.5",
@@ -42,9 +41,7 @@
   },
   "ava": {
     "require": [
-      "esm",
-      "core-js/features/array/flat",
-      "core-js/features/array/flat-map"
+      "esm"
     ]
   },
   "esm": {