remove absolute paths in SOURCES.txt

Author: rusty1s

setup.py

@@ -25,7 +25,7 @@
 def get_extensions():
     extensions = []
 
-    extensions_dir = osp.join(osp.dirname(osp.abspath(__file__)), 'csrc')
+    extensions_dir = osp.join('csrc')
     main_files = glob.glob(osp.join(extensions_dir, '*.cpp'))
 
     for main, suffix in product(main_files, suffices):