update readme deps versions

Author: mmckerns

README.md

@@ -137,9 +137,9 @@ Requirements
 
 * ``python`` (or ``pypy``), **==2.7** or **>=3.7**
 * ``setuptools``, **>=42**
-* ``pox``, **>=0.3.0**
-* ``dill``, **>=0.3.4**
-* ``ppft``, **>=1.6.6.4**
+* ``pox``, **>=0.3.1**
+* ``dill``, **>=0.3.5.1**
+* ``ppft``, **>=1.7.6.5**
 * ``multiprocess``, **>=0.70.12.1**