BUG: Links to different sub-directories broken in some cases

[AakashGfude]

In lecture https://julia.quantecon.org/dynamic_programming/perm_income.html the link this discussion has the link https://julia.quantecon.org/dynamic_programming/tools_and_techniques/linear_models.html#lm-fgs instead of https://julia.quantecon.org/tools_and_techniques/linear_models.html#lm-fgs

[mmcky]

@AakashGfude I think this is now resolve. Can this be closed?