Fixed form matcher specs

[Fedcomp]

This fixes failing tests in master. Possibly related to #12 😉
Rspec errors:

1) form matchers #have_field for form with invalid field return false
   Failure/Error: Hanami::Action::Params.new({})
   
   NoMethodError:
     undefined method `call' for nil:NilClass
     Did you mean?  caller
   # /home/user/.rvm/gems/ruby-2.3.1/gems/hanami-validations-1.0.0/lib/hanami/validations.rb:360:in `validate'
   # /home/user/.rvm/gems/ruby-2.3.1/gems/hanami-controller-1.0.1/lib/hanami/action/params.rb:72:in `initialize'
   # ./spec/support/views.rb:9:in `new'
   # ./spec/support/views.rb:9:in `params'
   # /home/user/.rvm/gems/ruby-2.3.1/gems/hanami-helpers-1.0.0/lib/hanami/helpers/form_helper/form_builder.rb:118:in `initialize'
   # /home/user/.rvm/gems/ruby-2.3.1/gems/hanami-helpers-1.0.0/lib/hanami/helpers/form_helper.rb:418:in `new'
   # /home/user/.rvm/gems/ruby-2.3.1/gems/hanami-helpers-1.0.0/lib/hanami/helpers/form_helper.rb:418:in `form_for'
   # ./spec/support/views.rb:13:in `form'
   # ./spec/rspec/hanami/matchers/form_matchers_spec.rb:64:in `block (4 levels) in <top (required)>'

Rspec command to reproduce:

rspec ./spec/rspec/hanami/matchers/form_matchers_spec.rb:63 # form matchers #have_field for form with invalid field return false

[davydovanton]

looks good for me, thanks!