Update dependencies, supported node versions

Author: jwagner

.travis.yml

@@ -1,9 +1,7 @@
 language: node_js
 node_js:
     - "node"
-    - "6"
-    - "5"
-    - "4"
+    - "lts/*"
 os:
   - linux
   - osx

index.js

@@ -2,7 +2,7 @@ var smartcrop = require('smartcrop');
 var sharp = require('sharp');
 
 function rgb2rgba(input) {
-  var output = new Buffer(input.length / 3 * 4);
+  var output = Buffer.alloc(input.length / 3 * 4);
   for (var i = 0; i < input.length; i += 3) {
     output[i / 3 * 4] = input[i];
     output[i / 3 * 4 + 1] = input[i + 1];