Fixed bug with deleting tags

@hishamelgezeery  it seems in schema.rb the create table "idea_tags" should be "ideas_tags" because that how it is used in the models.rb. 

So I only changed the name of the table idea_tags to ideas_tags as it caused an exception when deleting tags for some reason.

try this code if you want to check the error  in rails console: 
t = Tag.new
t.save
t.destroy