Ups I missed it 
I’ve resized the Droplet to 1Gb by the using SWAP and tried to rebuild it, but it didn’t help me. However, yesterday I rebuild it successfully.
if ($http_host != $$ENV_DISCOURSE_HOSTNAME) {
rewrite (.*) https://$$ENV_DISCOURSE_HOSTNAME$1 permanent;
} in /etc/nginx/conf.d/discourse.conf
I, [2016-07-27T06:45:30.779342 #13] INFO -- : > if [ -z "$LETSENCRYPT_ACCOUNT_EMAIL" ]; then echo "LETSENCRYPT_ACCOUNT_EMAIL ENV variable is required and has not been set."; exit 1; fi
I, [2016-07-27T06:45:30.782199 #13] INFO -- : LETSENCRYPT_ACCOUNT_EMAIL ENV variable is required and has not been set.
I, [2016-07-27T06:45:30.789702 #13] INFO -- : Terminating async processes
I, [2016-07-27T06:45:30.790433 #13] INFO -- : Sending INT to HOME=/var/lib/postgresql USER=postgres exec chpst -u postgres:postgres:ssl-cert -U postgres:postgres:ssl-cert /usr/lib/postgresql/9.5/bin/postmaster -D /etc/postgresql/9.5/main pid: 42
2016-07-27 06:45:30 UTC [42-2] LOG: received fast shutdown request
2016-07-27 06:45:30 UTC [42-3] LOG: aborting any active transactions
2016-07-27 06:45:30 UTC [49-2] LOG: autovacuum launcher shutting down
I, [2016-07-27T06:45:30.801912 #13] INFO -- : Sending TERM to exec chpst -u redis -U redis /usr/bin/redis-server /etc/redis/redis.conf pid: 155
155:signal-handler (1469601930) Received SIGTERM scheduling shutdown...
2016-07-27 06:45:30 UTC [46-1] LOG: shutting down
2016-07-27 06:45:30 UTC [46-2] LOG: database system is shut down
155:M 27 Jul 06:45:30.851 # User requested shutdown...
155:M 27 Jul 06:45:30.852 * Saving the final RDB snapshot before exiting.
155:M 27 Jul 06:45:30.990 * DB saved on disk
155:M 27 Jul 06:45:30.990 # Redis is now ready to exit, bye bye...
FAILED
--------------------
Pups::ExecError: if [ -z "$LETSENCRYPT_ACCOUNT_EMAIL" ]; then echo "LETSENCRYPT_ACCOUNT_EMAIL ENV variable is required and has not been set."; exit 1; fi failed with return #<Process::Status: pid 3087 exit 1>
Location of failure: /pups/lib/pups/exec_command.rb:108:in `spawn'
exec failed with the params {"cmd"=>["if [ -z \"$LETSENCRYPT_ACCOUNT_EMAIL\" ]; then echo \"LETSENCRYPT_ACCOUNT_EMAIL ENV variable is required and has not been set.\"; exit 1; fi", "/bin/bash -c \"if [[ ! \\\"$LETSENCRYPT_ACCOUNT_EMAIL\\\" =~ ([^@]+)@([^\\.]+) ]]; then echo \\\"LETSENCRYPT_ACCOUNT_EMAIL is not a valid email address\\\"; exit 1; fi\""]}
b723307a27a32d6c808e520b0cc3000fa2cbfe732291dd1bb312e7c9b8bfb375
** FAILED TO BOOTSTRAP ** please scroll up and look for earlier error messages, there may be more than one
root@discourse:/var/discourse#