Fix error caused by `honor_cipher_order`, CI errors

[jonnystorm]

OTP-22.1 (commit 124da8950c) introduced assert_role/4 into :ssl, which throws an error when :ssl.connect is called with the honor_cipher_order option defined. The error returned is {:error, {:option, :server_only, :honor_cipher_order}}.

With OTP-22.1, a dialyzer warning also appears:

    129: Invalid type specification for function
    hackney_ssl:shutdown/2. The success typing is
    ( { 'sslsocket',
         _,
         nonempty_maybe_improper_list()
      | {'dtls' | port(), _}
      },
      'read' | 'read_write' | 'write'
    ) -> 'ok' | {'error',_}

Prior to the above, CI errors began to appear as a result of cowboy-1.0.4 download failures. Using cowboy-1.1.2 fixes this.

• remove honor_cipher_order option in connect/4
• add OTP-22.0 to .travis.yml
• drop OTP-20.2 from .travis.yml (no longer available)
• fix invalid type spec for shutdown/2
• require cowboy-1.1.2