Change name of test directory.

test/run_unit.jl

test/simulation/plot_pkg.jl

test/simulation/plot_sync_doping_3way_oscillator.jl

test/simulation/plot_sync_repressilator.jl

test/simulation/sim_er.jl

test/simulation/sim_er_row_buffer_bounded.jl

test/simulation/sim_pm_er.jl

test/simulation/sim_pm_sync_er.jl

test/simulation/sim_poisson.jl

test/simulation/sim_repressilator.jl

test/simulation/sim_sir.jl

test/simulation/sim_sir_bounded.jl

test/simulation/sim_sir_col_buffer_bounded.jl

test/simulation/sim_sir_row_buffer_bounded.jl

test/simulation/sim_sir_tauleap.jl

test/unit/absorbing_x0.jl

test/unit/change_obs_var_sir.jl

test/unit/change_obs_var_sir_2.jl

test/unit/check_model_consistency.jl

test/unit/check_trajectory_consistency.jl