http2_adapter 2.9.0

What's new

• Expose supportedProtocols on ConnectionManager (defaults to ['h2'],
  fully backwards-compatible). Setting it to ['h2', 'http/1.1'] fixes
  fallbackAdapter silently never firing against RFC 7301-compliant servers
  that abort the TLS handshake with no_application_protocol when only h2
  is advertised.
• Fix socket leak: when DioH2NotSupportedException is thrown after a
  successful TLS handshake (server selected http/1.1 instead of h2),
  the SecureSocket is now explicitly destroyed before routing to
  fallbackAdapter, rather than being abandoned.
• Deprecate the misspelled ConnectionManager.handshakeTimout parameter in
  favor of the correctly spelled handshakeTimeout; the deprecated alias
  keeps working and is scheduled for removal in 3.0.0.