Fix collection page headers link 
Fix collection page headers link 

https://github.com/getgrav/grav/issues/672
getgrav/grav-learn,miljan-aleksic/grav-learn,miljan-aleksic/grav-learn,miljan-aleksic/grav-learn,Quy/grav-learn,miljan-aleksic/grav-learn,Quy/grav-learn,getgrav/grav-learn,getgrav/grav-learn,Quy/grav-learn,getgrav/grav-learn,Quy/grav-learn