python3: ValueError: Found array with dim 4. Estimator expected <= 2.
原因：维度不匹配。数组维度为4维，现在期望的是 <= 2维
方法：改为二维形式。
本人这里是4维度，我改为个数为两维度，如下处理：
source_x = (source_x.reshape(source_x.shape[0], source_x.shape[1] * source_x.shape[2] * source_x.shape[3])) target_x = (target_x.reshape(target_x.shape[0], target_x.shape[1] * target_x.shape[2] * target_x.shape[3])) 123
