Add Version Command

Addresses https://github.com/github/licensed/issues/62

Adds the "version" command. This command simply outputs the current
installed version of the gem.

README.md

@@ -74,9 +74,11 @@ Warnings:
 3 dependencies checked, 3 warnings found.
 ```
 
+- `licensed version`: Show current installed version of Licensed. Aliases: `-v|--version`
+
 ### Configuration
 
-All commands accept a `-c|--config` option to specify a path to a configuration file or directory.
+All commands, except `version`, accept a `-c|--config` option to specify a path to a configuration file or directory.
 
 If a directory is specified, `licensed` will look in that directory for a file named (in order of preference):
 1. `.licensed.yml`

lib/licensed.rb

@@ -17,4 +17,5 @@ require "licensed/configuration"
 require "licensed/command/cache"
 require "licensed/command/status"
 require "licensed/command/list"
+require "licensed/command/version"
 require "licensed/ui/shell"

lib/licensed/cli.rb

@@ -30,6 +30,13 @@ module Licensed
       run Licensed::Command::List.new(config)
     end
 
+    map "-v" => :version
+    map "--version" => :version
+    desc "version", "Show Installed Version of Licensed, [-v, --version]"
+    def version
+      run Licensed::Command::Version.new
+    end
+
     private
 
     # Returns a configuration object for the CLI command

lib/licensed/command/version.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+module Licensed
+  module Command
+    class Version
+      def initialize
+        @ui = Licensed::UI::Shell.new
+      end
+
+      def run
+        @ui.info(Licensed::VERSION)
+      end
+
+      def success?
+        true
+      end
+    end
+  end
+end

test/cli_test.rb

@@ -68,4 +68,18 @@ describe "licensed" do
       refute out =~ /Usage/i
     end
   end
+
+  describe "version" do
+    it "outputs VERSION constant" do
+      expected_out = "#{Licensed::VERSION}\n"
+      out, status = Open3.capture2 "bundle exec exe/licensed version"
+      assert_equal out, expected_out
+
+      out, status = Open3.capture2 "bundle exec exe/licensed -v"
+      assert_equal out, expected_out
+
+      out, status = Open3.capture2 "bundle exec exe/licensed --version"
+      assert_equal out, expected_out
+    end
+  end
 end