title: Keras - using activation function with a parameter
body: <p>How is it possible to use leaky ReLUs in the newest version of keras?
  Function relu() accepts an optional parameter 'alpha', that is responsible for the negative slope, but I cannot figure out how to pass ths paramtere when constructing a layer. </p>
  
  <p>This line is how I tried to do it,</p>
  
  <pre><code>model.add(Activation(relu(alpha=0.1))
  </code></pre>
  
  <p>but then I get the error</p>
  
  <pre><code>TypeError: relu() missing 1 required positional argument: 'x'
  </code></pre>
  
  <p>How can I use a leaky ReLU, or any other activation function with some parameter?</p>