fix typo

Author: bretello

src/prompt_toolkit/widgets/base.py

@@ -208,7 +208,7 @@ def __init__(
         if input_processors is None:
             input_processors = []
 
-        # Writeable attributes.
+        # Writable attributes.
         self.completer = completer
         self.complete_while_typing = complete_while_typing
         self.lexer = lexer