Fixed small bug in Appender class in docstring module.

Former Bug was that all strings will be append directly after old
docstring independent of self.join
Can be tested with matplotlib.pyplot.figimage.__doc__ where Appender
class has been used.

Author: cgringmuth

lib/matplotlib/docstring.py

@@ -87,7 +87,7 @@ def __init__(self, addendum, join=''):
 
     def __call__(self, func):
         docitems = [func.__doc__, self.addendum]
-        func.__doc__ = func.__doc__ and ''.join(docitems)
+        func.__doc__ = func.__doc__ and self.join.join(docitems)
         return func