Update horovod version to 0.15.2 (#182)

Author: Loquats

environment.yml

@@ -26,7 +26,7 @@ dependencies:
 - PyYAML=3.13
 - pip:
   # runtime
-  - horovod==0.15.0
+  - horovod==0.15.2
   # test
   - prospector==0.12.11
   - argh==0.26.2

python/requirements.txt

@@ -12,5 +12,5 @@ six>=1.10.0
 paramiko>=2.4.0
 PyNaCl==1.2.1 # Note: This is a transitive dependency of paramiko v 1.3.0 fails
 cloudpickle>=0.5.2
-horovod==0.15.0
+horovod==0.15.2
 wrapt==1.10.11