Buck build failed

**Describe the bug**

`buck build programs:zstd` results in

```
Buck wasn't able to parse zstd/lib/BUCK:
Syntax error on line 136, column 5:
srcs=['common/error_private.c'],
^

This error happened while trying to get dependency '//lib:mem' of target '//programs:zstd'
```

**To Reproduce**

Run `buck build programs:zstd` in the root dir.

**Expected behavior**

It should build.

**Screenshots and charts**

**Additional context**

The bug is clearly due to a missing comma before `srcs=`, which is introduced in v1.5.0.