fix path error to autodoc apis

docs/conf.py

@@ -12,6 +12,10 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
+import os
+import sys
+sys.path.insert(0, os.path.abspath('..'))
+
 version_file = '../mmcv/version.py'
 with open(version_file, 'r') as f:
     exec(compile(f.read(), version_file, 'exec'))