chore(coverage): enable branch coverage (#221)

Author: msabramo

Makefile

@@ -19,7 +19,7 @@ tests:
 	python radon/tests/run.py
 
 cov:
-	coverage erase && coverage run --include "radon/*" --omit "radon/__init__.py,radon/cli.py,radon/tests/*" radon/tests/run.py
+	coverage erase && coverage run --branch --include "radon/*" --omit "radon/__init__.py,radon/cli.py,radon/tests/*" radon/tests/run.py
 	coverage report -m
 
 htmlcov: cov