Update Exercise_04_2_solution.ipynb

fix solution

Author: jglombitza

Exercise_04_2_solution.ipynb

@@ -88,8 +88,8 @@
     "    def __init__(self, units=1, input_dim=1):  # when intializing the layer the weights have to be initialized\n",
     "        super(LinearLayer, self).__init__()\n",
     "        w_init = tf.random_normal_initializer()\n",
-    "        self.w = tf.Variable(initial_value=w_init(shape=(input_dim, units), dtype=\"float32\"),\n",
-    "                             trainable=True)\n",
+    "        self.w = self.add_weight(shape=(input_dim, units), initializer=w_init\n",
+    "                                 trainable=True)\n",
     "\n",
     "    def call(self, inputs):  # when calling the layer the linear transformation has to be performed\n",
     "        return tf.matmul(inputs, self.w)"