install.rb in mixlib-install-3.12.3

- old
+ new

@@ -16,10 +16,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
 
 require "mixlib/versioning"
-require "mixlib/shellout"
+require "mixlib/shellout" unless defined?(Mixlib::ShellOut)
 
 require_relative "install/backend"
 require_relative "install/options"
 require_relative "install/generator"
 require_relative "install/generator/bourne"