Bump Traefik to v1.3.8

Hello,

This PR updates Traefik to v1.3.8.

/cc @vdemeester @emilevauge

Cheers

library/traefik

@@ -10,10 +10,16 @@ Tags: v1.4.0-rc1-alpine, 1.4.0-rc1-alpine, v1.4-alpine, 1.4-alpine, roquefort-al
 GitCommit: e926214258069c7e7a8cf1e7cac8ad14d177b11f
 Directory: alpine
 
-Tags: v1.3.7, 1.3.7, v1.3, 1.3, raclette, latest
-GitCommit: 871d6c731511ed011b8b14fb6ae7942cc0df2929
-
-Tags: v1.3.7-alpine, 1.3.7-alpine, v1.3-alpine, 1.3-alpine, raclette-alpine
-GitCommit: 871d6c731511ed011b8b14fb6ae7942cc0df2929
-Directory: alpine
+Tags: v1.3.8, 1.3.8, v1.3, 1.3, raclette, latest
+Architectures: amd64, arm64v8, arm32v6
+GitCommit: 0d6fceb44fd48e7b05bffe13a1a6209dbee20c04
+amd64-Directory: scratch/amd64
+arm32v6-Directory: scratch/arm
+arm64v8-Directory: scratch/arm64
 
+Tags: v1.3.8-alpine, 1.3.8-alpine, v1.3-alpine, 1.3-alpine, raclette-alpine, alpine
+Architectures: amd64, arm64v8, arm32v6
+GitCommit: 0d6fceb44fd48e7b05bffe13a1a6209dbee20c04
+amd64-Directory: alpine/amd64
+arm32v6-Directory: alpine/arm
+arm64v8-Directory: alpine/arm64