Fix appveyor.yml (#1621)
Fix appveyor.yml (#1621)

Add escaping for sed command. Fixes #1611.
maruel/ninja,ndsol/subninja,ninja-build/ninja,ninja-build/ninja,ninja-build/ninja,Qix-/ninja,atetubou/ninja,iwadon/ninja,iwadon/ninja,ndsol/subninja,iwadon/ninja,AoD314/ninja,Qix-/ninja,bradking/ninja,AoD314/ninja,bradking/ninja,sgraham/ninja,ndsol/subninja,Qix-/ninja,maruel/ninja,maruel/ninja,atetubou/ninja,sgraham/ninja,iwadon/ninja,ndsol/subninja,atetubou/ninja,ninja-build/ninja,bradking/ninja,AoD314/ninja,AoD314/ninja,sgraham/ninja,sgraham/ninja,maruel/ninja,Qix-/ninja,atetubou/ninja,bradking/ninja