update tornado to 4.5.1 (#2754)

frameworks/Python/tornado/requirements_mongo.txt

@@ -1,2 +1,2 @@
-tornado==4.4.2
+tornado==4.5.1
 motor==1.1

frameworks/Python/tornado/requirements_pg.txt

@@ -1,2 +1,2 @@
-tornado==4.4.2
+tornado==4.5.1
 Momoko==2.2.4