chore: set Node.js compatibility to v6+

- drop support for versions less than Node v6 via engines
- update integration tests to also test newer versions

Author: ErisDS

README.markdown

@@ -79,7 +79,7 @@ Supported Environments
 
 Handlebars has been designed to work in any ECMAScript 3 environment. This includes
 
-- Node.js
+- Node.js v6+
 - Chrome
 - Firefox
 - Safari 5+

integration-testing/multi-nodejs-test/test.sh

@@ -17,7 +17,7 @@ cd "$( dirname "$( readlink -f "$0" )" )" || exit 1
 unset npm_config_prefix
 
 echo "Handlebars should be able to run in various versions of NodeJS"
-for i in  0.10 0.12 4 5 6 7 8 9 10 11 ; do
+for i in 6 7 8 9 10 11 12 13; do
     rm target node_modules package-lock.json -rf
     mkdir target
     nvm install "$i"

package.json

@@ -18,7 +18,7 @@
   "license": "MIT",
   "readmeFilename": "README.md",
   "engines": {
-    "node": ">=0.4.7"
+    "node": ">=6"
   },
   "dependencies": {
     "neo-async": "^2.6.0",