Merge pull request #10 from dkocic/dkocic-patch-1

Fixing command existence detection on Windows.

lib/av/cli.rb

@@ -20,7 +20,7 @@ def method_missing name, *args, &block
       end
 
       def detect_command(command)
-        command = "if command -v #{command} 2>/dev/null; then echo \"true\"; else echo \"false\"; fi"
+        command = self.system_based_detect_command(command)
         result = ::Av.run(command)
         case result
           when /true/
@@ -29,5 +29,13 @@ def detect_command(command)
             return false
         end
       end
+
+      def system_based_detect_command(command)
+        if Gem.win_platform?
+          "#{command} -version  2>NUL && echo true || echo false"
+        else
+          "if command -v #{command} 2>/dev/null; then echo \"true\"; else echo \"false\"; fi"
+        end
+      end
   end
 end