[rubygems/rubygems] Update comment by the review comment

https://github.com/rubygems/rubygems/commit/7c54dc56f6

lib/bundler/cli.rb

@@ -620,7 +620,7 @@ module Bundler
     method_option "dry-run", :type => :boolean, :default => false, :banner =>
       "Only print out changes, do not clean gems"
     method_option "force", :type => :boolean, :default => false, :banner =>
-      "Forces clean even if system location is used"
+      "Forces cleaning up unused gems even if Bundler is configured to use globally installed gems. As a consequence, removes all system gems except for the ones in the current application."
     def clean
       require_relative "cli/clean"
       Clean.new(options.dup).run

lib/bundler/man/bundle-clean.1

@@ -20,5 +20,5 @@ Print the changes, but do not clean the unused gems\.
 .
 .TP
 \fB\-\-force\fR
-Force a clean even if system location is used\.
+Forces cleaning up unused gems even if Bundler is configured to use globally installed gems\. As a consequence, removes all system gems except for the ones in the current application\.
 

lib/bundler/man/bundle-clean.1.ronn

@@ -15,4 +15,4 @@ useful when you have made many changes to your gem dependencies.
 * `--dry-run`:
   Print the changes, but do not clean the unused gems.
 * `--force`:
-  Force a clean even if system location is used.
+  Forces cleaning up unused gems even if Bundler is configured to use globally installed gems. As a consequence, removes all system gems except for the ones in the current application.