added back xgboost requirement

requirements.txt

@@ -8,4 +8,5 @@ scipy >= 0.19.0
 simpleutils >= 0.1.0
 sqlalchemy >= 1.1.14
 psycopg2 >= 2.7.1
-finance-python >= 0.5.7
\ No newline at end of file
+finance-python >= 0.5.7
+xgboost
\ No newline at end of file