only delete .rst and .png in the tests directory

tests/test_simple.py

@@ -1,19 +1,19 b''
 from nbconvert import ConverterRST
 import nose.tools as nt
 
 import os
 import glob
 
 def clean_dir():
     "Remove .rst files created during conversion"
-    map(os.remove, glob.glob("*.rst"))
-    map(os.remove, glob.glob("*.png"))
+    map(os.remove, glob.glob("./tests/*.rst"))
+    map(os.remove, glob.glob("./tests/*.png"))
 
 
 @nt.with_setup(clean_dir, clean_dir)
 def test_simple():
     fname = 'tests/test.ipynb'
     c = ConverterRST(fname)
     f = c.render()
     nt.assert_true('rst' in f, 'changed file extension to rst')