Update docker-library images

- `cassandra`: 2.2.8
- `mongo`: 3.3.15

library/cassandra

@@ -5,17 +5,17 @@ Maintainers: Tianon Gravi <[email protected]> (@tianon),
 GitRepo: https://github.com/docker-library/cassandra.git
 
 Tags: 2.1.15, 2.1
-GitCommit: ef66ec669d3930aea018f74dc58f5bd2ef5df880
+GitCommit: ef57ef961003e27469b86178f0b4d184bb64d82e
 Directory: 2.1
 
-Tags: 2.2.7, 2.2, 2
-GitCommit: ef66ec669d3930aea018f74dc58f5bd2ef5df880
+Tags: 2.2.8, 2.2, 2
+GitCommit: ef57ef961003e27469b86178f0b4d184bb64d82e
 Directory: 2.2
 
 Tags: 3.0.9, 3.0
-GitCommit: caf1d916f7ffaecef5685668a878495dc6222537
+GitCommit: ef57ef961003e27469b86178f0b4d184bb64d82e
 Directory: 3.0
 
 Tags: 3.7, 3, latest
-GitCommit: c3c26f2efdb9874dc5b3717662462e8ca0b2d944
+GitCommit: ef57ef961003e27469b86178f0b4d184bb64d82e
 Directory: 3.7

library/mongo

@@ -26,11 +26,11 @@ GitCommit: 89549b2b779421c057b04858477012b7aa17f498
 Directory: 3.2/windows/windowsservercore
 Constraints: windowsservercore
 
-Tags: 3.3.14, 3.3
-GitCommit: abe4de7ed3e951c3c37cdab0891914aca3f99fef
+Tags: 3.3.15, 3.3
+GitCommit: 944c44b6304ab387e4640fddaa808bc93f32b176
 Directory: 3.3
 
-Tags: 3.3.14-windowsservercore, 3.3-windowsservercore
-GitCommit: abe4de7ed3e951c3c37cdab0891914aca3f99fef
+Tags: 3.3.15-windowsservercore, 3.3-windowsservercore
+GitCommit: 944c44b6304ab387e4640fddaa808bc93f32b176
 Directory: 3.3/windows/windowsservercore
 Constraints: windowsservercore