Add spec to the result of Coverage lib for begin

Ref: jruby/jruby#8173
This commit is intended to make sure `Coverage` library behaves
the same for the code with `begin`. JRuby had an issue so this
change will help JRuby and other implementations to avoid it.

library/coverage/code_with_begin_spec.rb

@@ -0,0 +1,24 @@
+require_relative '../../spec_helper'
+require 'coverage'
+
+describe 'Coverage for the code with begin' do
+  before :all do
+    @file = fixture __FILE__, 'code_with_begin.rb'
+  end
+
+  after :each do
+    $LOADED_FEATURES.delete(@file)
+  end
+
+  it 'covers 100% lines' do
+    Coverage.start
+    require @file.chomp('.rb')
+    result = Coverage.result
+
+    result.should == {
+      @file => [
+        nil, 1, nil
+      ]
+    }
+  end
+end

library/coverage/fixtures/code_with_begin.rb

@@ -0,0 +1,3 @@
+begin
+  puts 'begin'
+end