Fails to detect on some modules

#### Current behavior :

`rqmts.py` fails to detect packages which have different names.

#### Expected behavior :

Successfully detects and parses out the dependency _(package version)_

#### Logcat

```
C:\Users\rqmts>py -3 rqmts.py
Enter path of the python script : C:\tests\run.py
[!] System package: `re`
[!] System package: `time`
[!] System package: `string`
[!] System package: `strgen` <---- NOT A SYSTEM PACKAGE
[!] System package: `random`
[!] System package: `os`
[!] System package: `time`
[+] Success: Parsed the dependencies correctly
[*] Saving generated requirements.txt
[+] Success: requirements.txt saved
[+] Path where it can be found: C:\tests\requirements.txt
```

#### References :

1. **[pypi-strgen](https://pypi.org/project/StringGenerator/)**
2. `pip install StringGenerator`

查看 rqmts.py 以了解它如何检测系统包与外部依赖项。问题是 'strgen'（来自 PyPI 包 StringGenerator）被错误地标记为系统包。检查区分内置模块与 PyPI 包的逻辑，可能通过与标准库模块列表进行比较来实现。通过在导入 strgen 的文件上运行脚本来测试以验证修复。

由索引模型根据 Issue 内容生成。