Improve small details in specs:

* Fix coding standards;
* Simplify some expectations (eq instead of be matcher);
* Expect identity on block instead of calling;
* Change some before call as oneliners;
* Avoid shadowing variable names;
* Improve wording where needed.

spec/support/net_ssh_story_helpers.rb

@@ -36,7 +36,7 @@ module NetSSHStoryHelpers
   def sftp_story
     story do |session|
       ch = session.opens_channel
-      ch.sends_subsystem('sftp')
+      ch.sends_subsystem 'sftp'
       ch.sends_packet(
         Net::SFTP::Constants::PacketTypes::FXP_INIT, :long,
         Net::SFTP::Session::HIGHEST_PROTOCOL_VERSION_SUPPORTED

spec/support/tests_helpers.rb

@@ -1,9 +1,9 @@
 module TestsHelpers
   def test_ok
-    double('test', pass?: true)
+    double 'test', pass?: true
   end
 
   def test_ko
-    double('test', pass?: false)
+    double 'test', pass?: false
   end
 end