Set DYLD_LIBRARY_PATH for OSX

Signed-off-by: Dan O'Reilly <oreilldf@gmail.com>

python/tox.ini

diff --git a/python/tox.ini b/python/tox.ini
index d758512..9a934d0 100644
--- a/python/tox.ini
+++ b/python/tox.ini
@@ -9,6 +9,7 @@
 usedevelop=true
 setenv =
     cpp: LD_LIBRARY_PATH={toxinidir}/../src/.libs
+    cpp: DYLD_LIBRARY_PATH={toxinidir}/../src/.libs
     cpp: PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=cpp
 commands =
     python setup.py -q build_py