FIX: `RailsMultisite::ConnectionManagement#establish_connection` raises error on "default".

FIX: RailsMultisite::ConnectionManagement#establish_connection raises error on “default”.

diff --git a/lib/rails_multisite/connection_management.rb b/lib/rails_multisite/connection_management.rb
index 45b11c2..092bd8e 100644
--- a/lib/rails_multisite/connection_management.rb
+++ b/lib/rails_multisite/connection_management.rb
@@ -160,10 +160,14 @@ module RailsMultisite
     def establish_connection(opts)
       opts[:db] = opts[:db].to_s
 
-      spec = connection_spec(opts)
-      if (!spec && opts[:raise_on_missing])
-        raise "ERROR: #{opts[:db]} not found!"
+      if opts[:db] != DEFAULT
+        spec = connection_spec(opts)
+
+        if (!spec && opts[:raise_on_missing])
+          raise "ERROR: #{opts[:db]} not found!"
+        end
       end
+
       spec ||= @default_spec
       handler = nil
       if spec != @default_spec
diff --git a/spec/connection_management_spec.rb b/spec/connection_management_spec.rb
index 6cfa745..8b65bec 100644
--- a/spec/connection_management_spec.rb
+++ b/spec/connection_management_spec.rb
@@ -69,7 +69,11 @@ describe RailsMultisite::ConnectionManagement do
 
     before do
       conn.config_filename = fixture_path("two_dbs.yml")
-      conn.establish_connection(db: RailsMultisite::ConnectionManagement::DEFAULT)
+
+      conn.establish_connection(
+        db: RailsMultisite::ConnectionManagement::DEFAULT,
+        raise_on_missing: true
+      )
     end
 
     after do

GitHub sha: bb40fa08