Fixed __all__ -- should fixed pull request test on github

Author: jauy123

package/MDAnalysis/web/__init__.py

@@ -1,7 +1,7 @@
 from .downloaders import PdbDownloader
 from .functions import fetch_pdb
 
-__all__ = [fetch_pdb, PdbDownloader]
+__all__ = ['fetch_pdb', 'PdbDownloader']