Minor fixes to vulnerability plotting

bob/pad/base/script/__init__.py

+import numpy as np
+
+
 def remove_nan(scores):
     """Removes the NaNs from the scores
 

bob/pad/base/script/plots.py

@@ -226,7 +226,7 @@ def common_options(f):
         '--subplot', type=INT, default=111,
         show_default=True, help='The order of subplots.')(f)
     f = click.option(
-        '-o', '--output', type=File(mode='w'),
+        '-o', '--output', type=File(mode='wb'),
         default='plots.pdf', show_default=True,
         help='The file to save the plots in.')(f)
     f = click.argument('scores', nargs=-1)(f)