Code enhancement #201

 * version is now required
 * better error handling
 * etc...

Signed-off-by: Chin Yeung Li <tli@nexb.com>

Author: chinyeungli

src/fetchcode/download_urls.py

@@ -21,8 +21,8 @@
 from fetchcode.cpan import CPAN
 from fetchcode.cran import CRAN
 from fetchcode.huggingface import Huggingface
-from fetchcode.pypi import Pypi
 from fetchcode.nix import Nix
+from fetchcode.pypi import Pypi
 
 package_registry = [Pypi, CRAN, CPAN, Huggingface, Composer, Nix]