Fix to print version when version option is passed

Before this commit

```
$ lrama --version
File should be specified
```

After

```
$ lrama --version
lrama 0.5.4
```

lib/lrama/command.rb

@@ -5,7 +5,6 @@ class Command
     def initialize(argv)
       @argv = argv
 
-      @version = nil
       @skeleton = "bison/yacc.c"
       @header = false
       @header_file = nil
@@ -23,11 +22,6 @@ def initialize(argv)
     def run
       parse_option
 
-      if @version
-        puts Lrama::VERSION
-        exit 0
-      end
-
       Report::Duration.enable if @trace_opts[:time]
 
       warning = Lrama::Warning.new
@@ -113,7 +107,7 @@ def parse_option
       opt = OptionParser.new
 
       # opt.on('-h') {|v| p v }
-      opt.on('-V', '--version') {|v| @version = true }
+      opt.on('-V', '--version') {|v| puts "lrama #{Lrama::VERSION}"; exit 0 }
 
       # Tuning the Parser
       opt.on('-S', '--skeleton=FILE') {|v| @skeleton = v }

spec/lrama/command_spec.rb

@@ -1,4 +1,15 @@
+require "open3"
+
 RSpec.describe Lrama::Command do
+  describe "version option" do
+    it "print Lrama version and exit" do
+      result = Open3.popen3("ruby", exe_path("lrama"), "--version") do |stdin, stdout, stderr, wait_thr|
+        stdout.read
+      end
+      expect(result).to eq("lrama #{Lrama::VERSION}\n")
+    end
+  end
+
   describe "#run" do
     describe "a grammar file is specified" do
       it "ends successfully" do

spec/spec_helper.rb

@@ -30,3 +30,7 @@
 def fixture_path(file_name)
   File.expand_path("../fixtures/#{file_name}", __FILE__)
 end
+
+def exe_path(file_name)
+  File.expand_path("../../exe/#{file_name}", __FILE__)
+end