[pica-etherpad-db] Fix error in Dockerfile

pica-etherpad-db/Dockerfile

@@ -5,7 +5,7 @@ COPY config/binary_log.cnf /etc/mysql/conf.d/binary_log.cnf
 # By default, COPY uses permissions `-rw-rw-rw-` for the file inside
 # the container. But mysql refuses to use config files that are world-
 # writable, so we have to change those permissions:
-RUN chmod 644 /etc/mysql/conf.d/limit_binary_log.cnf
+RUN chmod 644 /etc/mysql/conf.d/binary_log.cnf
 
 # Remove unnecessary tools
 # This removes the following packages: