keyword, add CONFLICT to postgres keywords

As in ON CONFLICT

Author: j-martin

sqlparse/keywords.py

@@ -834,6 +834,7 @@ def is_keyword(value):
 
 # PostgreSQL Syntax
 KEYWORDS_PLPGSQL = {
+    'CONFLICT': tokens.Keyword,
     'WINDOW': tokens.Keyword,
     'PARTITION': tokens.Keyword,
     'OVER': tokens.Keyword,