Require Node.js 6

package.json

@@ -5,7 +5,7 @@
 	"license": "MIT",
 	"repository": "chalk/chalk",
 	"engines": {
-		"node": ">=4"
+		"node": ">=6"
 	},
 	"scripts": {
 		"test": "xo && nyc ava && tsc --project types && flow --max-warnings=0",
@@ -43,26 +43,22 @@
 	"dependencies": {
 		"ansi-styles": "^3.2.1",
 		"escape-string-regexp": "^1.0.5",
-		"supports-color": "^5.3.0"
+		"supports-color": "^5.5.0"
 	},
 	"devDependencies": {
-		"ava": "0.25.0",
-		"coveralls": "^3.0.0",
-		"execa": "^0.10.0",
-		"flow-bin": "^0.73.0",
+		"ava": "^0.25.0",
+		"coveralls": "^3.0.2",
+		"execa": "^1.0.0",
+		"flow-bin": "^0.81.0",
 		"import-fresh": "^2.0.0",
 		"matcha": "^0.7.0",
-		"nyc": "^11.0.2",
+		"nyc": "^13.0.1",
 		"resolve-from": "^4.0.0",
-		"typescript": "^2.5.3",
-		"xo": "0.20.3"
+		"typescript": "^3.0.3",
+		"xo": "^0.23.0"
 	},
 	"types": "types/index.d.ts",
 	"xo": {
-		"envs": [
-			"node",
-			"mocha"
-		],
 		"ignores": [
 			"test/_flow.js"
 		]