rethinkdb_dart 2.3.2+6

Dart 2 driver for RethinkDB v2.3.

2.3.2+6

• Fix '_GrowableList
• Changed pbkdf2 package to pbkdf2_dart

2.3.2+5

• Made 'SocketException: OS Error: Connection refused' handleable by user code

2.3.2+4

• Fixed connection close listener
• Fixed connection test according to JavaScript driver

2.3.2+3

• Initial release (driver updated to Dart 2 and Flutter)