Ignore DevDependencies when generating template. (facebook#20542)

Summary:
Regarding [Add devDependenices support for templates](facebook@c4ab03a).

Once a project is created using the custom template command with devDependencies inside, the devDependenices.json file is also copied to the new projects directory.

By adding this to the ignore paths we stop the devDependenices being copied into the new projects directory.
Pull Request resolved: facebook#20542

Differential Revision: D9182795

Pulled By: hramos

fbshipit-source-id: 543c8ca67612a981c22fc83c8d54a25ddc0ca5fc

Author: TomAtterton

local-cli/generator/templates.js

@@ -171,7 +171,7 @@ function createFromRemoteTemplate(
       // only for publishing the template to npm.
       // We want to ignore this dummy file, otherwise it would overwrite
       // our project's package.json file.
-      ignorePaths: ['package.json', 'dependencies.json'],
+      ignorePaths: ['package.json', 'dependencies.json','devDependencies.json'],
     });
     installTemplateDependencies(templatePath, yarnVersion);
     installTemplateDevDependencies(templatePath, yarnVersion);