[Rails5] Fix running spinach tests

1. Add support for `RAILS5=1|true` for the `bin/spinach` command.
2. Synchronize used spinach versions both for rails4 and rails5.

For rails5 it was accidently used spinach 0.10.1 instead of 0.8.10.
That brought some problems on running spinach tests.

Example of failure message:

NoMethodError: undefined method `line' for #<Spinach::Scenario:0x000000000c86ba80>
Did you mean?  lines
  /builds/gitlab-org/gitlab-ce/features/support/env.rb:52:in `before_scenario_run'

Gemfile.rails5.lock

@@ -321,6 +321,9 @@ GEM
       rubyntlm (~> 0.5)
     globalid (0.4.1)
       activesupport (>= 4.2.0)
+    goldiloader (2.0.1)
+      activerecord (>= 4.2, < 5.2)
+      activesupport (>= 4.2, < 5.2)
     gollum-grit_adapter (1.0.1)
       gitlab-grit (~> 2.7, >= 2.7.1)
     gollum-lib (4.2.7)
@@ -878,7 +881,7 @@ GEM
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.2)
     slack-notifier (1.5.1)
-    spinach (0.10.1)
+    spinach (0.8.10)
       colorize
       gherkin-ruby (>= 0.3.2)
       json
@@ -1072,6 +1075,7 @@ DEPENDENCIES
   gitlab-markup (~> 1.6.2)
   gitlab-styles (~> 2.3)
   gitlab_omniauth-ldap (~> 2.0.4)
+  goldiloader (~> 2.0)
   gollum-lib (~> 4.2)
   gollum-rugged_adapter (~> 0.4.4)
   gon (~> 6.1.0)

bin/spinach

 #!/usr/bin/env ruby
+
+# Remove this block when removing rails5? code.
+gemfile = %w[1 true].include?(ENV["RAILS5"]) ? "Gemfile.rails5" : "Gemfile"
+ENV['BUNDLE_GEMFILE'] ||= File.expand_path("../#{gemfile}", __dir__)
+
 begin
   load File.expand_path('../spring', __FILE__)
 rescue LoadError => e