What was the change in the Weighted-Average Grant-Date Fair Value for nonvested shares in 2019 from 2018?
{"Nonvested at fiscal year end 2018": {"Shares": 1631470.0, "Weighted-Average Grant-Date Fair Value": 75.39}, "Granted": {"Shares": 692899.0, "Weighted-Average Grant-Date Fair Value": 77.77}, "Vested": {"Shares": -689040.0, "Weighted-Average Grant-Date Fair Value": 70.31}, "Forfeited": {"Shares": -232910.0, "Weighted-Average Grant-Date Fair Value": 78.8}, "Nonvested at fiscal year end 2019": {"Shares": 1402419.0, "Weighted-Average Grant-Date Fair Value": 78.36}}
nonvested_2019_weighted_average_grant_date_fair_value = df["Nonvested at fiscal year end 2019"]["Weighted-Average Grant-Date Fair Value"]
nonvested_2018_weighted_average_grant_date_fair_value = df["Nonvested at fiscal year end 2018"]["Weighted-Average Grant-Date Fair Value"]
answer = nonvested_2019_weighted_average_grant_date_fair_value - nonvested_2018_weighted_average_grant_date_fair_value