Wrong in Chapter 3, "tidb-kv-to-relation" part

[hanhy611]

the index sample was wrong:
t10_i1_10_1 --> null
t10_i1_20_2 --> null
t10_i1_30_3 --> null

should be:
t10_i1_10_1_1 --> t10_r1
t10_i1_20_2_1 --> t10_r2
t10_i1_30_3_1 --> t10_r3