Require lingua for tests.

setup.py

diff --git a/setup.py b/setup.py
index 93f861a..11dbb14 100644
--- a/setup.py
+++ b/setup.py
@@ -47,7 +47,7 @@
       url='http://www.makotemplates.org/',
       license='MIT',
       packages=find_packages('.', exclude=['examples*', 'test*']),
-      tests_require=['nose >= 0.11', 'mock', 'Babel'],
+      tests_require=['nose >= 0.11', 'mock', 'Babel', 'lingua'],
       test_suite="nose.collector",
       zip_safe=False,
       install_requires=install_requires,