@almazkaist these specs are not passing

```
$ be rspec spec/models/tag_spec.rb 
Rack::File headers parameter replaces cache_control after Rack 1.5.
F.F

Failures:

  1) Tag 
     Failure/Error: it { should has_many(:projects) }
     NoMethodError:
       undefined method `has_many' for #<RSpec::Core::ExampleGroup::Nested_1:0x007fe28706f498>
     # ./spec/models/tag_spec.rb:4:in `block (2 levels) in <top (required)>'

  2) Tag 
     Failure/Error: it { should has_many(:projects_tags) }
     NoMethodError:
       undefined method `has_many' for #<RSpec::Core::ExampleGroup::Nested_1:0x007fe286fb8b08>
     # ./spec/models/tag_spec.rb:5:in `block (2 levels) in <top (required)>'

Finished in 0.03643 seconds
3 examples, 2 failures

Failed examples:

rspec ./spec/models/tag_spec.rb:4 # Tag 
rspec ./spec/models/tag_spec.rb:5 # Tag 

Randomized with seed 18948
```