Small fixes for SASL Plain connection

[y-lan]

Hi thanks for the great library !

I found some small problems when using it to connect to a HiveServer2 with LDAP auth. So I made some fixes. Please check it.

• hash.symbolize_keys is a rails function, changed it to pure ruby implementation
• SaslClientTransport should be created after symbolize_keys

[andytinycat]

Thanks for the fix.