Update ruby Docker tag to v2.6

renovate-bot · renovate-bot · commit 34147946425e · 2018-12-27T23:00:28.000Z
diff --git a/Dockerfile b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:2.5
+FROM ruby:2.6
 
 RUN mkdir /app
 WORKDIR /app
