Avoid using deprecated Buffer API on newer Node.js

This avoids using Buffer constructor API on newer Node.js versions.

To achieve that, Buffer.from presence is checked, with validation that it's
not the same method as Uint8Array.from.

Refs:
https://nodejs.org/api/deprecations.html#deprecations_dep0005_buffer_constructor

index.js

@@ -280,7 +280,14 @@ function decodefield (str) {
       value = getlatin1(binary)
       break
     case 'utf-8':
-      value = new Buffer(binary, 'binary').toString('utf8')
+      if (Buffer.from && Buffer.from !== Uint8Array.from) {
+        // Node.js 4.5.0 or newer
+        value = Buffer.from(binary, 'binary').toString('utf8')
+      } else {
+        // Old Node.js versions
+        // `binary` is always a string here, so this is safe
+        value = new Buffer(binary, 'binary').toString('utf8')
+      }
       break
     default:
       throw new TypeError('unsupported charset in extended field')