Add new "rake fastly:purge" command for purging Fastly cache
Add new "rake fastly:purge" command for purging Fastly cache

  This is useful when making changes to the code that cause
  sudden changes in the displayed badge level.

  This isn't tested yet, so there may be further changes to come.

Signed-off-by: David A. Wheeler <9ae72d22d8b894b865a7a496af4fab6320e6abb2@dwheeler.com>

coreinfrastructure/best-practices-badge,wanganyv/cii-best-practices-badge,dwvisser/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,linuxfoundation/cii-best-practices-badge,wanganyv/cii-best-practices-badge,jdossett/cii-best-practices-badge,coreinfrastructure/best-practices-badge,taylorcoursey/cii-best-practices-badge,coreinfrastructure/best-practices-badge,wanganyv/cii-best-practices-badge,dwvisser/cii-best-practices-badge,linuxfoundation/cii-best-practices-badge,linuxfoundation/cii-best-practices-badge,linuxfoundation/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,dwvisser/cii-best-practices-badge,jdossett/cii-best-practices-badge,yannickmoy/cii-best-practices-badge,yannickmoy/cii-best-practices-badge,wanganyv/cii-best-practices-badge,yannickmoy/cii-best-practices-badge,dwvisser/cii-best-practices-badge,jdossett/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,jdossett/cii-best-practices-badge,coreinfrastructure/best-practices-badge,yannickmoy/cii-best-practices-badge