[ja] Apply c8571b3b9b7890e6da9d3823c13aed0079e8f257
[ja] Apply fbc3502da99c415d3aa38bcb11758e4e479594de
[ja] Apply bc3f922f2549e44524dc11301d1e53c984b14a1b
[ja] Apply fa4f5a44e26b4a695d65561f6ee4da1954b583ab
[ja] Apply a8203518ecb201bb551586a2ff982832c29ddbd5
Merge pull request #410 from harupong/ja-chapter8

[ja] Update chapter8