Attempt to fix the "I should see that I am [un]subscribed" steps

Makes use of Capybara methods that wait. Hopefully this will fix the
random timing-related failures of this step.

features/steps/project/issues/issues.rb

@@ -19,12 +19,11 @@ class Spinach::Features::ProjectIssues < Spinach::FeatureSteps
   end
   step 'I should see that I am subscribed' do
-    expect(find(".subscribe-button span").text).to eq "Unsubscribe"
+    expect(find('.subscribe-button span')).to have_content 'Unsubscribe'
   end
   step 'I should see that I am unsubscribed' do
-    sleep 0.2
-    expect(find(".subscribe-button span").text).to eq "Subscribe"
+    expect(find('.subscribe-button span')).to have_content 'Subscribe'
   end
   step 'I click link "Closed"' do

features/steps/project/merge_requests.rb

@@ -58,11 +58,11 @@ class Spinach::Features::ProjectMergeRequests < Spinach::FeatureSteps
   end
   step 'I should see that I am subscribed' do
-    expect(find(".subscribe-button span").text).to eq "Unsubscribe"
+    expect(find('.subscribe-button span')).to have_content 'Unsubscribe'
   end
   step 'I should see that I am unsubscribed' do
-    expect(find(".subscribe-button span")).to have_content("Subscribe")
+    expect(find('.subscribe-button span')).to have_content 'Subscribe'
   end
   step 'I click button "Unsubscribe"' do