Update Elixir to 1.9

Fix #9

Dockerfile

@@ -1,4 +1,4 @@
-FROM elixir:1.8-alpine
+FROM elixir:1.9-alpine
 
 ENV UID=911 GID=911 \
     MIX_ENV=prod
@@ -7,14 +7,14 @@ ARG PLEROMA_VER=develop
 
 RUN apk -U upgrade \
     && apk add --no-cache \
-       build-base \
-       git
+    build-base \
+    git
 
 RUN addgroup -g ${GID} pleroma \
     && adduser -h /pleroma -s /bin/sh -D -G pleroma -u ${UID} pleroma
 
 USER pleroma
-WORKDIR pleroma
+WORKDIR /pleroma
 
 RUN git clone -b develop https://git.pleroma.social/pleroma/pleroma.git /pleroma \
     && git checkout ${PLEROMA_VER}