Update changelog.

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Revision history for `pandocfilters`
 
+-  v1.5.1
+   - Don't raise an error if the directory used to store images already exists (#104, Augusto Zanellato).
+
 -  v1.5.0: Last release supporting Python 2.
    - Added an environment variable `PANDOCFILTER_CLEANUP` that when `get_filename4code` is used, temporary directory will be cleaned up automatically. See #88.
    - `examples/` is no longer included in the distribution (i.e. source distribution or binary wheels found on PyPI.) This should be a backward compatible change as `examples/` is never exposed as a Python module, nor entry points.