[llvm-readobj] Fix JSON output for Relocations

The existing JSON incorrectly outputs line breaks and other invalid JSON.

Example Before this patch:

```
...
"Relocations":[Section (9) .rela.dyn {
  0xA3B0 R_X86_64_RELATIVE - 0x43D0
  0xA3B8 R_X86_64_RELATIVE - 0x4A30
...
```

Example After this patch:

```
...
"Relocations":[Section (9) .rela.dyn {
{"Relocation":{"Offset":41904,"Type":{"Value":"R_X86_64_RELATIVE","RawValue":8},
"Symbol":{"Value":"","RawValue":0},"Addend":17360}},
{"Relocation":{"Offset":41912,"Type":{"Value":"R_X86_64_RELATIVE","RawValue":8},
"Symbol":{"Value":"","RawValue":0},"Addend":18992}},
{"Relocation":{"Offset":41920,"Type":{"Value":"R_X86_64_RELATIVE","RawValue":8},
"Symbol":{"Value":"","RawValue":0},"Addend":17440}},
...
```

Note there are still issues with the Section, but each Relocation is
now a valid JSON object that can be parsed. Future patches will address
the issues regarding JSON output for the Section.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D137089