bump alpine to 3.8 and klar to 2.2.0

Dockerfile

@@ -4,14 +4,14 @@
 #     go build
 #     docker build --rm=true -t jmccann/drone-clair .
 
-FROM alpine:3.4
+FROM alpine:3.8
 
 RUN apk update && \
   apk add \
     ca-certificates && \
   rm -rf /var/cache/apk/*
 
-ADD https://github.com/optiopay/klar/releases/download/v1.1/klar-1.1-linux-amd64 /usr/local/bin/klar
+ADD https://github.com/optiopay/klar/releases/download/v2.2.0/klar-2.2.0-linux-amd64 /usr/local/bin/klar
 RUN chmod 0755 /usr/local/bin/klar
 
 ADD drone-clair /bin/