The column name of the LOOKUP on edge result changed

[randomJoe211]

Nebula Graph version: 2.5.0

As tested and documented in the LOOKUP doc, the result of `LOOKUP on like should be:

nebula)> LOOKUP ON like;
+-------------+----------+-------------+
| _src        | _ranking | _dst        |
+-------------+----------+-------------+
| "player100" | 0        | "player101" |
+-------------+----------+-------------+

But the column names has changed in 2.5.0:

(root@nebula) [basketballplayer]> lookup on follow
+-------------+-------------+---------+
| SrcVID      | DstVID      | Ranking |
+-------------+-------------+---------+
| "player100" | "player101" | 0       |
+-------------+-------------+---------+
| "player100" | "player125" | 0       |
+-------------+-------------+---------+
...

We are not aware that this happened until just a Nebula user found this issue and submitted a PR to modify the doc.

[CPWstatic]

This was introduced in the first version of 2.0.0. We should update the docs.

[randomJoe211]

Updated in master doc.