Fix spelling in description (#10)

Co-authored-by: Dustin Ingram <di@users.noreply.github.com>

Author: brainwane

setup.py

@@ -12,7 +12,7 @@
 setup(
     name='trove-classifiers',
     version='2020.04.01',
-    description="Cannonical source for classifiers on PyPI (pypi.org).",
+    description="Canonical source for classifiers on PyPI (pypi.org).",
     long_description=long_description,
     long_description_content_type="text/markdown",
     url="https://github.com/pypa/trove-classifiers",