replace plugin generator USAGE "script/rails" which are removed by r16868

git-svn-id: http://svn.redmine.org/redmine/trunk@17132 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/generators/redmine_plugin/USAGE

@@ -2,7 +2,7 @@ Description:
     The plugin generator creates stubs for a new Redmine plugin.
 
 Example:
-    ./script/rails generate redmine_plugin meetings
+    bundle exec rails generate redmine_plugin meetings
       create  plugins/meetings/app
       create  plugins/meetings/app/controllers
       create  plugins/meetings/app/helpers

lib/generators/redmine_plugin_controller/USAGE

@@ -2,4 +2,4 @@ Description:
     Generates a plugin controller.
 
 Example:
-    ./script/rails generate redmine_plugin_controller meetings pools index show vote
+    bundle exec rails generate redmine_plugin_controller meetings pools index show vote

lib/generators/redmine_plugin_model/USAGE

@@ -2,4 +2,4 @@ Description:
     Generates a plugin model.
 
 Examples:
-    ./script/rails generate redmine_plugin_model meetings pool
+    bundle exec rails generate redmine_plugin_model meetings pool