Raise end-index by 1 when setting range-parts

This commit fixes a bug in Range, leading to the last line of a Range
not being able to be replaced via the __setitem__-function as the final
line setting its contents in the buffer the Range is based on assumes the
end-index to be inclusive, which it isn't in Python-slicing-notation.

neovim/api/buffer.py

@@ -160,8 +160,8 @@ def __setitem__(self, idx, lines):
         if start is None:
             start = self.start
         if end is None:
-            end = self.end + 1
-        self._buffer[start:end] = lines
+            end = self.end
+        self._buffer[start:end + 1] = lines
 
     def __iter__(self):
         for i in range(self.start, self.end + 1):