Fixed whitespace issues in gitian-build.sh
Fixed whitespace issues in gitian-build.sh

Summary: Original file has an awful mix of tabs and spaces, making it completely unreadable.

Test Plan: Read it.

Reviewers: deadalnix, schancel, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D2136

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