Bump alpine to 3.11

There's a new release which appears to have no apparent down-
sides or breakages.

https://www.alpinelinux.org/posts/Alpine-3.11.2-released.html

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

sample-functions/HostnameIntent/Dockerfile

@@ -1,4 +1,7 @@
 FROM functions/alpine:latest
+
+USER root
+
 RUN apk --update add nodejs nodejs-npm
 
 COPY package.json   .
@@ -6,5 +9,8 @@ COPY handler.js     .
 COPY sample.json    .
 
 RUN npm i
+
+USER 1000
+
 ENV fprocess="node handler.js"
 CMD ["fwatchdog"]