Try to fix Docker build by removing empty continuation lines.

Thanks to xet7 !

Dockerfile

@@ -175,24 +175,19 @@ RUN \
     set -o xtrace && \
     # Add non-root user wekan
     useradd --user-group --system --home-dir /home/wekan wekan && \
-    \
     # OS dependencies
     apt-get update -y && apt-get install -y --no-install-recommends ${BUILD_DEPS} && \
-    \
     # Meteor installer doesn't work with the default tar binary, so using bsdtar while installing.
     # https://github.com/coreos/bugs/issues/1095#issuecomment-350574389
     cp $(which tar) $(which tar)~ && \
     ln -sf $(which bsdtar) $(which tar) && \
-    \
     # Download nodejs
     wget https://nodejs.org/dist/${NODE_VERSION}/node-${NODE_VERSION}-${ARCHITECTURE}.tar.gz && \
     wget https://nodejs.org/dist/${NODE_VERSION}/SHASUMS256.txt.asc && \
     #---------------------------------------------------------------------------------------------
-    \
     # Verify nodejs authenticity
     grep ${NODE_VERSION}-${ARCHITECTURE}.tar.gz SHASUMS256.txt.asc | shasum -a 256 -c - && \
     rm -f SHASUMS256.txt.asc && \
-    \
     # Install Node
     tar xvzf node-${NODE_VERSION}-${ARCHITECTURE}.tar.gz && \
     rm node-${NODE_VERSION}-${ARCHITECTURE}.tar.gz && \
@@ -201,13 +196,10 @@ RUN \
     ln -s /opt/nodejs/bin/npm /usr/bin/npm && \
     mkdir -p /opt/nodejs/lib/node_modules/fibers/.node-gyp /root/.node-gyp/${NODE_VERSION} /home/wekan/.config && \
     chown wekan --recursive /home/wekan/.config && \
-    \
     #DOES NOT WORK: paxctl fix for alpine linux: https://github.com/wekan/wekan/issues/1303
     #paxctl -mC `which node` && \
-    \
     # Install Node dependencies. Python path for node-gyp.
     npm install -g npm@${NPM_VERSION} && \
-    \
     # Change user to wekan and install meteor
     cd /home/wekan/ && \
     chown wekan --recursive /home/wekan && \
@@ -215,11 +207,9 @@ RUN \
     gosu wekan:wekan curl https://install.meteor.com/ | /bin/sh && \
     mv /root/.meteor /home/wekan/ && \
     chown wekan --recursive /home/wekan/.meteor && \
-    \
     sed -i 's/api\.versionsFrom/\/\/api.versionsFrom/' /home/wekan/app/packages/meteor-useraccounts-core/package.js && \
     cd /home/wekan/.meteor && \
     gosu wekan:wekan /home/wekan/.meteor/meteor -- help; \
-    \
     # Build app
     cd /home/wekan/app && \
     mkdir -p /home/wekan/.npm && \
@@ -236,10 +226,8 @@ RUN \
     # Remove legacy webbroser bundle, so that Wekan works also at Android Firefox, iOS Safari, etc.
     rm -rf /home/wekan/app_build/bundle/programs/web.browser.legacy && \
     mv /home/wekan/app_build/bundle /build && \
-    \
     # Put back the original tar
     mv $(which tar)~ $(which tar) && \
-    \
     # Cleanup
     apt-get remove --purge -y ${BUILD_DEPS} && \
     apt-get autoremove -y && \
@@ -250,12 +238,11 @@ RUN \
     rm -R /home/wekan/app && \
     rm -R /home/wekan/app_build && \
     mkdir /data && \
-    chown wekan --recursive /data && \
+    chown wekan --recursive /data
     #cat /home/wekan/python/esprima-python/files.txt | xargs rm -R && \
     #rm -R /home/wekan/python
     #rm /home/wekan/install_meteor.sh
 
-
 ENV PORT=8080
 EXPOSE $PORT
 USER wekan