ActiveRecord::ConnectionTimeoutError with Sinatra

I am running a modular Sinatra app with ActiveRecord with SQLite on development. I keep on running into ActiveRecord::ConnectionTimeoutError could not obtain a database connection within 5.000 seconds (waited 5.001 seconds) after exceeding my connection pool size.

I have tried all the following methods:

1. use ActiveRecord::ConnectionAdapater::ConnectionManagement from here
2. after { ActiveRecord::Base.connection.close } from here
3. ActiveRecord::Base.clear_active_connections! from here

However, I still keep on getting the same errors!

 # Gemfile
source 'https://rubygems.org'
ruby '2.0.0'

gem 'activerecord', '~> 4.0.2'
gem 'sass', '~> 3.2.12'
gem 'sinatra', '~> 1.4.4'
gem 'sinatra-activerecord'
gem 'sinatra-assetpack', '~> 0.3.1'
gem 'sinatra-contrib', '~> 1.4.2'
gem 'slim', '~> 2.0.2'

group :development do
  gem 'tux'
  gem 'sqlite3'
end

group :production do
  gem 'pg'
end

group :test do
  gem 'database_cleaner'
  gem 'factory_girl', '~> 4.3.0'
  gem 'rspec'
end

# environments.rb
config :development do
  ActiveRecord::Base.establish_connection(
    adapter: 'sqlite3',
    database: 'local.db'
  )
end