Remove extra spaces in template.rb (#1422)

Currently it adds an extra indent level in a new webpacker Rails project's development.rb and production.rb, so the `config` statement doesn't line up with the others.

lib/install/template.rb

@@ -19,7 +19,7 @@
 
 check_yarn_integrity_config = ->(value) { <<CONFIG }
 # Verifies that versions and hashed value of the package contents in the project's package.json
-  config.webpacker.check_yarn_integrity = #{value}
+config.webpacker.check_yarn_integrity = #{value}
 CONFIG
 
 if Rails::VERSION::MAJOR >= 5