mention that `ipython notebook --pylab` will be disabled

IPython/html/notebookapp.py

@@ -523,7 +523,8 b' class NotebookApp(BaseIPythonApplication):'
         self.kernel_argv = swallow_argv(self.argv, notebook_aliases, notebook_flags)
         if any(arg.startswith(u'--pylab') for arg in self.kernel_argv):
             self.log.warn('\n    '.join([
-                "Starting all kernels in pylab mode is not recommended.",
+                "Starting all kernels in pylab mode is not recommended,",
+                "and will be disabled in a future release.",
                 "Please use the %matplotlib magic to enable matplotlib instead.",
                 "pylab implies many imports, which can have confusing side effects",
                 "and harm the reproducibility of your notebooks.",