Fix typo in Dockerfile

pica-oh-my-form/Dockerfile

@@ -13,7 +13,7 @@ RUN apk add --no-cache python=2.7.16-r1 \
 
 RUN wget -O omf.tar.gz https://github.com/ohmyform/ohmyform/archive/${OHMYFORM_VERSION}.tar.gz \
   && tar --strip-components=1 -x -f omf.tar.gz -C /opt/app \
-  && mkdir -p /opt/app/public/lib
+  && mkdir -p /opt/app/public/lib \
   && chown -R ohmyform:ohmyform /opt/app
 
 WORKDIR /opt/app