Addressed "FutureWarning: 'Y-DEC' is deprecated and will be removed i…

…n a future version, please use 'YE-DEC' instead."

chainladder/core/triangle.py

@@ -690,7 +690,7 @@ def grain(self, grain="", trailing=False, inplace=False):
  obj = self.dev_to_val()
 
  if ograin_new != ograin_old:
- freq = {"Y": "Y", "S": "2Q"}.get(ograin_new, ograin_new)
+ freq = {"Y": "YE", "S": "2Q"}.get(ograin_new, ograin_new)
 
  if trailing or (obj.origin.freqstr[-3:] != "DEC" and ograin_old != "M"):
  origin_period_end = self.origin[-1].strftime("%b").upper()