Add CHANGELOG for #100

Author: nicoddemus

CHANGELOG.rst

@@ -1,9 +1,11 @@
-1.6.3 (08-08-2019)
+1.7.0 (08-08-2019)
 ------------------
 
 * `#102 <https://github.com/pytest-dev/execnet/pull/102>`__: Show paths in stack traces
   generated by ``remote_exec()``.
 
+* `#100 <https://github.com/pytest-dev/execnet/pull/100>`__: Fix flaky hangs in ``workerpool.waitall``.
+
 1.6.1 (2019-07-22)
 ------------------