Don't overwrite config with default values

otherwise users are obliged to set the config values *after* sourcing
the plugin. They're not able to do it before. Also, re-sourcing the
plugin will reset the values to the defaults again.

See zimfw/zimfw#301

Fixes #335

spec/spec_helper.rb

@@ -11,8 +11,8 @@ RSpec.shared_context 'terminal session' do
 
   around do |example|
     before_sourcing.call
-
-    session.run_command((['source zsh-autosuggestions.zsh'] + options).join('; '))
+    session.run_command(options.join('; '))
+    session.run_command('source zsh-autosuggestions.zsh')
     after_sourcing.call
     session.clear_screen