Update "docker" submodule to latest hepdata-converter-docker version.

GraemeWatt · GraemeWatt · commit 48587f2dd181 · 2018-07-19T16:01:38.000+01:00
diff --git a/docker b/docker
@@ -1 +1 @@
-Subproject commit 392cb55e270da261726f556abfb98fc1767ccea4
+Subproject commit a7d7cbad39ddbc5feea4272a38b42048da30eb47
