fixed Docker build for bpkg

Dockerfile

@@ -17,6 +17,7 @@ RUN add-apt-repository ppa:webupd8team/java -y && apt-get update && apt-get -y i
 #RUN rm -rf /var/www/html/ui && mv ui /var/www/html/ && chown www-data:www-data /var/www/html/ui
 
 # use bpkg to handle complex bash entrypoints
+ENV USER=root
 RUN curl -Lo- "https://raw.githubusercontent.com/bpkg/bpkg/master/setup.sh" | bash
 RUN bpkg install cha87de/bashutil -g
 ## add more bash dependencies, if necessary