Sample code for c in memory-leak-in-c is wrong

It is just document typo in https://fbinfer.com/docs/all-issue-types#memory-leak-in-c

Bellow code is not legal c-syntax.

```c
-(void) memory_leak_bug {
struct Person *p = malloc(sizeof(struct Person));
}
```

I think it should be:

```c
void memory_leak_bug () {
struct Person *p = malloc(sizeof(struct Person));
}
```

Please include the following information:
- [-] The version of infer from `infer --version`.
- [-] Your operating system and version, for example "Debian 9", "MacOS High Sierra", whether you are using Docker, etc.
- [-] Which command you ran, for example `infer -- make`.
- [-] The full output in a paste, for instance a [gist](https://gist.github.com/).
- [-] If possible, a minimal example to reproduce your problem (for instance, some code where
infer reports incorrectly, together with the way you run infer to reproduce the incorrect
report).