Update and rename test_fbprophet.py to test_prophet.py

Matches the new package name from #1150

Author: rosbo

tests/test_fbprophet.py renamed to tests/test_prophet.py

@@ -5,7 +5,7 @@
 
 from prophet import Prophet
 
-class TestFbProphet(unittest.TestCase):
+class TestProphet(unittest.TestCase):
     def test_fit(self):
         train = pd.DataFrame({
             'ds': np.array(['2012-05-18', '2012-05-20']),