Enable Capybara/CurrentPathExpectation cop & fix issues

Read cop description http://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/Capybara/CurrentPathExpectation to better understand reasons behind enforcing this rule

On some cases the `only_path: true` was needed as argument of `have_current_path` matcher to avoid comparing the url parameters and just checking the path.

spec/features/budgets/ballots_spec.rb

@@ -310,7 +310,7 @@ feature 'Ballots' do
       click_link group.name
       # No need to click on the heading name
       expect(page).to have_content("Investment projects with scope: #{heading.name}")
-      expect(current_path).to eq(budget_investments_path(budget))
+      expect(page).to have_current_path(budget_investments_path(budget), only_path: true)
     end
 
     scenario 'Displaying the correct group, heading, count & amount' do
@@ -378,7 +378,7 @@ feature 'Ballots' do
       find(".remove-investment-project").trigger('click')
     end
 
-    expect(current_path).to eq(budget_ballot_path(budget))
+    expect(page).to have_current_path(budget_ballot_path(budget))
     expect(page).to have_content("You have voted 0 investments")
   end
 

spec/features/budgets/investments_spec.rb

@@ -279,7 +279,7 @@ feature 'Budget Investments' do
 
       expect(page.status_code).to eq(200)
       expect(page.html).to be_empty
-      expect(current_path).to eq(budget_investments_path(budget_id: budget.id))
+      expect(page).to have_current_path(budget_investments_path(budget_id: budget.id))
     end
 
     scenario 'Create budget investment too fast' do
@@ -296,7 +296,7 @@ feature 'Budget Investments' do
       click_button 'Create Investment'
 
       expect(page).to have_content 'Sorry, that was too quick! Please resubmit'
-      expect(current_path).to eq(new_budget_investment_path(budget_id: budget.id))
+      expect(page).to have_current_path(new_budget_investment_path(budget_id: budget.id))
     end
 
     scenario 'Create' do