update tp102-how-to-use-git-github.md

[callmePicacho]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

修复有个文本错误，这个错误导致 markdown 语法无法成功渲染文本

2. What did you expect to see?

3. What did you see instead?

在文档中：
正确文本应当是：**Suggested Assignments:**，而非：**Suggested Assignments: **
前者冒号后面多出来的空格，将导致文本无法被加粗

[callmePicacho]

问题产生在 tp102-how-to-use-git-github.md 文档中 36 行的 **Suggested Assignments: **