DOC: add changelog message

Author: jairideout

ChangeLog.md

@@ -14,6 +14,7 @@ Bug fixes
 * The ``--similarity`` option in ``pick_otus.py`` now only accepts sequence similarity thresholds between 0.0 and 1.0 (inclusive). Previous behavior would allow values outside this range, which would cause uninformative error messages to be raised by the external tools that ``pick_otus.py`` wraps ([#1979](https://github.com/biocore/qiime/issues/1979)).
 * ``split_libraries_fastq.py`` now explicitly disallows ``-p 0``. This could lead to empty sequences being written to the resulting output file ([#1984](https://github.com/biocore/qiime/issues/1984)).
 * Fixed issued where ``filter_samples_from_otu_table.py`` could only filter the mapping file when ``--valid_states`` was passed as the filtering method ([#2003](https://github.com/biocore/qiime/issues/2003)).
+* Fixed bug where distance matrix files generated by QIIME (e.g., using ``beta_diversity.py``) could have diagonals with values that were close to zero in rare cases (depending on input data, machine architecture, installed dependencies, etc.). These files could not be loaded by QIIME scripts that accepted distance matrix files as input (e.g., ``principal_coordinates.py``) and would result in an error message stating that the distance matrix was not hollow. Values on the diagonal that are close to zero are now set to 0.0 ([#1933](https://github.com/biocore/qiime/issues/1933)).
 
 
 Usability enhancements