Switch to Node v6 as the oldest version we support

Removed a deprecation notice I added in an earlier commit (ef1c59072c).

.travis.yml

@@ -3,7 +3,6 @@ node_js:
 - 9 # Current stable 
 - 8 # Active LTS until April 2019
 - 6 # Active LTS until April 2018
-- 4 # Maintenance LTS until 2018-04-01, will be dropped in The Lounge v3
 
 matrix:
   fast_finish: true

appveyor.yml

@@ -11,7 +11,7 @@ skip_tags: true
 skip_branch_with_pr: true
 
 environment:
-  nodejs_version: '4'
+  nodejs_version: '6'
 
 install:
   - ps: Install-Product node $env:nodejs_version

package.json

@@ -35,7 +35,7 @@
   ],
   "license": "MIT",
   "engines": {
-    "node": ">=4.2.0"
+    "node": ">=6"
   },
   "dependencies": {
     "bcryptjs": "2.4.3",

src/command-line/index.js

@@ -10,11 +10,6 @@ const colors = require("colors/safe");
 const Helper = require("../helper");
 const Utils = require("./utils");
 
-if (require("semver").lt(process.version, "6.0.0")) {
-	log.warn(`Support of Node.js v4 is ${colors.bold.red("deprecated")} and will be removed in The Lounge v3.`);
-	log.warn("Please upgrade to Node.js v6 or more recent.");
-}
-
 program.version(Helper.getVersion(), "-v, --version")
 	.option("--home <path>", `${colors.bold.red("[DEPRECATED]")} Use the ${colors.green("THELOUNGE_HOME")} environment variable instead.`)
 	.option(