Fix errors due to the toml gem doesn't dump array of table correctly

See jm/toml#31

features/support/env.rb

@@ -129,8 +129,11 @@ def edit_hub_config
     hub_config = []
     yield hub_config
 
-    data = { :credentials => hub_config }
-    File.open(config, 'w') { |cfg| cfg << TOML::Generator.new(data).body }
+    # the `toml` gem doesn't work well with array of table (https://github.com/mojombo/toml#array-of-tables)
+    # a temporary solution here to output the right format
+    # see https://github.com/jm/toml/issues/31
+    data = hub_config.map { |c| "[[credentials]]\n#{TOML::Generator.new(c).body}" }.join("\n\n")
+    File.open(config, 'w') { |cfg| cfg << data }
   end
 
   define_method(:text_editor_script) do |bash_code|