ode_transformer.py: Add missing colon on line 330

[wushuangX]

        self.calculate_num = args.enc_calculate_num
        self.rk_type = args.rk_type
         
        if self.calculate_num == 2 and self.rk_type == "learnable":
            # RK2-learnable
            self.gate_linear = Linear(2 * embed_dim, 1)
        elif self.calculate_num == 2 and self.rk_type == "initialization"
            self.alpha = torch.nn.Parameter(torch.Tensor(self.calculate_num))
            self.alpha.data.fill_(1)
        else:
            raise ValueError("invalid rk_type！")

        self.use_word_dropout = args.use_word_dropout
        self.word_dropout = args.word_dropout

I'm currently learning from your ODE transformer implementation, and I believe there might be a missing colon on line 330 of fairseq/models/ode_transformer.py. This co//uld potentially lead to an error during execution.