Fix broken link in flatten option documentation
Fix broken link in flatten option documentation

Set correct link to "Building the files object dynamically"
xetryj/assemble,assemble/grunt-assemble,davidwickman/assemble,valentinvieriu/assemble,assemble/grunt-assemble,cgvarela/assemble,valentinvieriu/assemble,a0000001/test,cgvarela/assemble,assemble/assemble,assemble/assemble,makotot/assemble,edrohler/assemble,davidwickman/assemble,edrohler/assemble,avr/assemble,xetryj/assemble