"Disable" composer bucket if php is not installed

lib/vagrant-cachier/cap/linux/composer_path.rb

@@ -4,8 +4,14 @@ module VagrantPlugins
       module Linux
         module ComposerPath
           def self.composer_path(machine)
-            composer_path = '/home/vagrant/.composer'
+            composer_path = nil
-            return composer_path 
+            machine.communicate.tap do |comm|
+              return unless comm.test('which php')
+              comm.execute 'echo $HOME' do |buffer, output|
+                composer_path = output.chomp if buffer == :stdout
+              end
+            end
+            return "#{composer_path}/.composer"
           end
         end
       end