correct two typos and remote random spaces.

Looked at the error output for https://travis-ci.org/net-ssh/net-ssh/jobs/30066590 and saw mention of issue at

```
Error: test_next_packet_with_aes256_gcm_openssh_com_and_none_and_standard_compression(Transport::TestPacketStream)

NoMethodError: undefined method `[]' for nil:NilClass

/home/travis/build/net-ssh/net-ssh/test/transport/test_packet_stream.rb:1704:in `block (4 levels) in <class:TestPacketStream>'
```

Looked at HMAC transport code and saw that it expects a hash as its parameter, not a string.