Наконец-то я решил добавить 'username: postgres' и 'password: ***' в общую часть config базы данных.yml;
default: &default
adapter: postgresql
encoding: unicode
# For details on connection pooling, see Rails configuration guide
# http://guides.rubyonrails.org/configuring.html#database-pooling
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
username: postgres
password: ***
Не в части разработки;
development:
<<: *default
database: CigBackCount_development
# The specified database role being used to connect to postgres.
# To create additional roles in postgres see `$ createuser --help`.
# When left blank, postgres will use the default role. This is
# the same name as the operating system user that initialized the database.
#username: CigBackCount
# The password associated with the postgres role (username).
#password:
После внесенных изменений я перезагрузил БД;
pg_ctl reload