resolved OpenCVImageViewer import error and added close method for gy…

…m viewer compatibility

dm2gym/envs/dm_suite_env.py

@@ -68,7 +68,7 @@ def render(self, mode='human', **kwargs):
                     from gym.envs.classic_control import rendering
                     self.viewer = rendering.SimpleImageViewer(maxwidth=1024)
                 else:
-                    from dm2gym import OpenCVImageViewer
+                    from . import OpenCVImageViewer
                     self.viewer = OpenCVImageViewer()
             self.viewer.imshow(img)
             return self.viewer.isopen

dm2gym/envs/opencv_image_viewer.py

@@ -10,6 +10,7 @@ class OpenCVImageViewer():
     This class is meant to be a drop-in replacement for
     `gym.envs.classic_control.rendering.SimpleImageViewer`
     """
+
     def __init__(self, *, escape_to_exit=False):
         """Construct the viewing window"""
         self._escape_to_exit = escape_to_exit
@@ -29,8 +30,11 @@ def imshow(self, img):
         # Listen for escape key, then exit if pressed
         if cv2.waitKey(1) in [27] and self._escape_to_exit:
             exit()
-    
+
     @property
     def isopen(self):
         """Is the window open?"""
         return self._isopen
+
+    def close(self):
+        pass