alpinelinux link changed

trying to use the Dockerfile, I had to update the link to make it work.

Author: evandor

plugins/Dockerfile

@@ -1,6 +1,6 @@
 FROM alpine:3.6
 
-RUN apk --no-cache add --repository http://dl-cdn.alpinelinux.org/alpine/3.6/community wget ca-certificates
+RUN apk --no-cache add --repository http://dl-4.alpinelinux.org/alpine/v3.6/community wget ca-certificates
 
 WORKDIR /tmp/sonarqube/plugins
 RUN wget https://github.com/Sagacify/sonar-scala/releases/download/v0.0.3/sonar-scala-plugin-0.0.3.jar