Make DeviceGray the default color as it should be

pdfminer/pdfcolor.py

@@ -23,12 +23,12 @@ class PDFColorSpace(object):
 
 PREDEFINED_COLORSPACE = collections.OrderedDict()
 for (name, n) in [
+    ('DeviceGray', 1),  # default value first
     ('CalRGB', 3),
     ('CalGray', 1),
     ('Lab', 3),
     ('DeviceRGB', 3),
     ('DeviceCMYK', 4),
-    ('DeviceGray', 1),
     ('Separation', 1),
     ('Indexed', 1),
     ('Pattern', 1),