Fix typo, newline is needed guysoft/OctoPi#807 (comment)

Author: guysoft

src/modules/base/start_chroot_script

@@ -12,7 +12,7 @@ export LC_ALL=C
 source /common.sh
 install_cleanup_trap
 if [ -n "${BASE_APT_MIRROR}" ]; then
-   echo -n "${BASE_APT_MIRROR}" | cat - /etc/apt/sources.list > /tmp/filename.tmp
+   echo "${BASE_APT_MIRROR}" | cat - /etc/apt/sources.list > /tmp/filename.tmp
    mv /tmp/filename.tmp /etc/apt/sources.list
 fi