Use size diff from root ref

[Hitenjain14]

Changes

Fixes

Tests

Tasks to complete before merging PR:

• [ ] Ensure system tests are passing. If not Run them manually to check for any regressions :clipboard:
• [ ] Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• [ ] Merge your system tests PR to master AFTER merging this PR

Associated PRs (Link as appropriate):

• 0chain:
• gosdk:
• system_test:
• zboxcli:
• zwalletcli:
• Other: ...

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.

Project coverage is 14.79%. Comparing base (e5018a7) to head (16e6dd0). Report is 93 commits behind head on staging.

Files	Patch %	Lines
...et/blobbercore/handler/object_operation_handler.go	0.00%	21 Missing :warning:
...ain.net/blobbercore/allocation/allocationchange.go	0.00%	9 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## staging #1460 +/- ## =========================================== - Coverage 14.88% 14.79% -0.10% =========================================== Files 179 180 +1 Lines 20222 20218 -4 =========================================== - Hits 3011 2991 -20 - Misses 16839 16857 +18 + Partials 372 370 -2 ``` | [Flag](https://app.codecov.io/gh/0chain/blobber/pull/1460/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=0chain) | Coverage Δ | | |---|---|---| | [Unit-Tests](https://app.codecov.io/gh/0chain/blobber/pull/1460/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=0chain) | `14.79% <0.00%> (-0.10%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=0chain#carryforward-flags-in-the-pull-request-comment) to find out more.

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