Use Buffer.from instead of deprecated new Buffer

Fixes #27

Declare minimum supported node version as 6 according to
https://nodejs.org/en/docs/guides/buffer-constructor-deprecation/#variant-1

Author: Mingun

KaitaiStream.js

@@ -622,8 +622,7 @@ KaitaiStream.bytesToStr = function(arr, encoding) {
         case 'ucs-2':
         case 'utf16le':
         case 'utf-16le':
-          return new Buffer(arr).toString(encoding);
-          break;
+          return Buffer.from(arr).toString(encoding);
         default:
           // unsupported encoding, we'll have to resort to iconv-lite
           if (typeof KaitaiStream.iconvlite === 'undefined')

package.json

@@ -22,6 +22,9 @@
   "devDependencies": {
     "jest": "^28.1.3"
   },
+  "engines": {
+    "node": ">=6.0.0"
+  },
   "keywords": [
     "binary",
     "file",