fix(rubocop): fix violations using `rubocop -a`

```bash
Inspecting 5 files
Scanning /home/imran/Salt/formulas/haproxy-formula/Gemfile
.Scanning /home/imran/Salt/formulas/haproxy-formula/bin/kitchen
.Scanning /home/imran/Salt/formulas/haproxy-formula/test/integration/default/controls/config.rb
CScanning /home/imran/Salt/formulas/haproxy-formula/test/integration/default/controls/package.rb
CScanning /home/imran/Salt/formulas/haproxy-formula/test/integration/default/controls/service.rb
C

Offenses:

test/integration/default/controls/config.rb:1:1: C: Style/FrozenStringLiteralComment: Missing frozen string literal comment.
title 'Verify haproxy configuration'
^
test/integration/default/controls/config.rb:9:1: C: Layout/TrailingEmptyLines: 1 trailing blank lines detected.
test/integration/default/controls/package.rb:1:1: C: Style/FrozenStringLiteralComment: Missing frozen string literal comment.
title 'Verify haproxy installation'
^
test/integration/default/controls/package.rb:4:1: C: Layout/IndentationWidth: Use 2 (not 4) spaces for indentation.
    it { should be_installed }
^^^^
test/integration/default/controls/package.rb:6:1: C: Layout/TrailingEmptyLines: 1 trailing blank lines detected.
test/integration/default/controls/service.rb:1:1: C: Style/FrozenStringLiteralComment: Missing frozen string literal comment.
title 'Verify haproxy service'
^
test/integration/default/controls/service.rb:8:1: C: Layout/TrailingEmptyLines: 2 trailing blank lines detected.

5 files inspected, 7 offenses detected
```

test/integration/default/controls/config.rb

+# frozen_string_literal: true
+
 title 'Verify haproxy configuration'
 
 describe file('/etc/haproxy/haproxy.cfg') do
@@ -6,4 +8,3 @@ describe file('/etc/haproxy/haproxy.cfg') do
   its('group') { should eq 'root' }
   its('mode') { should cmp '0644' }
 end
-

test/integration/default/controls/package.rb

+# frozen_string_literal: true
+
 title 'Verify haproxy installation'
 
 describe package('haproxy') do
   it { should be_installed }
 end
-

test/integration/default/controls/service.rb

+# frozen_string_literal: true
+
 title 'Verify haproxy service'
 
 describe service('haproxy') do
@@ -5,5 +7,3 @@ describe service('haproxy') do
   it { should be_enabled }
   it { should be_running }
 end
-
-