I am using it in https://reviews.llvm.org/D69399.
This change changes how obj2yaml dumps arrays of `llvm::yaml::Hex8/llvm::yaml::Hex16/llvm::yaml::Hex32`
from:
```
PayloadBytes:
- 0x01
- 0x02
...
```
To
```
PayloadBytes: [ 0x01, 0x02, ... ]
```
The latter way is shorter and looks better for arrays.
Differential revision: https://reviews.llvm.org/D69558
