fixes in PyBullet deep_mimic to allow running in pip version

examples/pybullet/gym/pybullet_envs/deep_mimic/learning/nets/fc_2layers_1024units.py

@@ -1,5 +1,5 @@
 import tensorflow as tf
-import learning.tf_util as TFUtil
+import pybullet_envs.deep_mimic.learning.tf_util as TFUtil
 
 NAME = "fc_2layers_1024units"
 

examples/pybullet/gym/pybullet_envs/deep_mimic/learning/nets/net_builder.py

@@ -1,4 +1,4 @@
-import learning.nets.fc_2layers_1024units as fc_2layers_1024units
+import pybullet_envs.deep_mimic.learning.nets.fc_2layers_1024units as fc_2layers_1024units
 
 def build_net(net_name, input_tfs, reuse=False):
     net = None