fixed URL on github.io

github.io moved to https and http returns 301 redirect
Fix misspellings in gitignore plugin
Fix gitignore curl, should follow redirects
Follow-redirect and silent mode curl throughout gitignore

This commit completes previous efforts and standardizes both curl commands
into using silent mode and following redirects in case the URL changes
again in the future.
Merge pull request #3226 from mcornella/fix-plugin-gitignore

[Plugin: gitignore] Several fixes in the plugin