Change licence to license to remove build warning

Author: chrisruk

setup.py

@@ -17,7 +17,7 @@
 setup(name='buildhat',
       version=version,
       description='Build HAT Python library',
-      licence='MIT',
+      license='MIT',
       long_description=long_description,
       long_description_content_type="text/markdown",
       author='Raspberry Pi Foundation',