fix axis label (#81)

Author: HumphreyYang

lectures/french_rev.md

@@ -855,8 +855,8 @@ plt.plot(bal[31:44], infl[31:44], '+', color='red', label='恐怖时期')
 plt.plot(bal[44:63], infl[44:63], '*', 
     color='orange', label='经典的Cagan恶性通货膨胀')
 plt.plot(bal[44:63], a3 + bal[44:63] * b3, color='orange')
-plt.xlabel('real balances')
-plt.ylabel('inflation')
+plt.xlabel('实际余额')
+plt.ylabel('通货膨胀')
 plt.legend()
 plt.tight_layout()
 plt.show()