Fix issue where tesseract langages weren't installed properly

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.7
+FROM alpine:3.8
 
 LABEL maintainer="The Paperless Project https://github.com/danielquinn/paperless" \
       contributors="Guy Addadi <[email protected]>, Pit Kleyersburg <[email protected]>, \
@@ -12,11 +12,10 @@ COPY scripts/docker-entrypoint.sh /sbin/docker-entrypoint.sh
 ENV PAPERLESS_EXPORT_DIR=/export \
     PAPERLESS_CONSUMPTION_DIR=/consume
 
-# Install dependencies
-RUN apk --no-cache --update add \
-        python3 gnupg libmagic bash shadow curl \
+
+RUN apk update --no-cache && apk add python3 gnupg libmagic bash shadow curl \
         sudo poppler tesseract-ocr imagemagick ghostscript unpaper && \
-    apk --no-cache add --virtual .build-dependencies \
+    apk add --virtual .build-dependencies \
         python3-dev poppler-dev gcc g++ musl-dev zlib-dev jpeg-dev && \
 # Install python dependencies
     python3 -m ensurepip && \