That will only prevent installation of master of the package or the immediate next few versions on 0.7. The old package versions without a julia upper bound remain available so users on 0.7 or 1.0 will just be held back to old versions of JuliaDB until a new release without an upper bound gets made.
https://github.com/JuliaComputing/JuliaDB.jl/commit/8bf3057d...
A automatic check as in R would indeed a better choice.