[chronik-docs] Trim to version number in installation steps

Summary:
The version file might contain whitespaces which would break the installation instructions/links, so trim it.
Also remove the newline in the sample file for good measure.

Test Plan: Deploy and check the installation instructions and links are properly generated even when the version file has whitespaces/newlines.

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D16044