[FIX] util/modules: fix wrong usage of warnings filtering

It's `catch_warnings` not `catchwarnings`
https://docs.python.org/2/library/warnings.html#warnings.catch_warnings
https://docs.python.org/3/library/warnings.html#warnings.catch_warnings

The context manager is meant to allow for specific filters that would be
reverted once it exists. This patch corrects the usage.

Oversight of fbd0b4f

closes #342

Signed-off-by: Alvaro Fuentes Suarez (afu) <afu@odoo.com>

Author: aj-fuentes

src/util/modules.py

@@ -310,7 +310,8 @@ def uninstall_theme(cr, theme, base_theme=None):
         for website in websites:
             IrModuleModule._theme_remove(website)
     flush(env_["base"])
-    with warnings.catchwarnings(action="ignore", category=UpgradeWarning):
+    with warnings.catch_warnings():
+        warnings.filterwarnings(action="ignore", category=UpgradeWarning)
         uninstall_module(cr, theme)