Use set -e instead of argument

This is better idea as having #!/bin/bash -e is fragile. Anyone can run
this script with bash -x file and that way unintentionally disable -e
flag.

generate_lists

-#!/bin/bash -e
+#!/bin/bash
 # Updater-ng configuration lists generating script
 # (C) 2018 CZ.NIC, z.s.p.o.
 #
@@ -14,6 +14,7 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
+set -e
 
 output_path=
 fallback=

generate_medkit

-#!/bin/bash -e
+#!/bin/bash
 # Turris medkit generator script
 # (C) 2018 CZ.NIC, z.s.p.o.
 #
@@ -14,6 +14,7 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
+set -e
 
 export BOARD=
 export BRANCH=