Use flow cli repo version.txt in install.sh

[sukantoraymond]

Closes #602

This PR changes version checking from google cloud version.txt to flow cli repo version.txt in install.sh and install.ps1

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[gpavlov2016]

I'm concerned about a situation where someone pushes an update to master with version update but does not release a new package right away to google - we will have a mismatch again.
More robust solution would be implementing verification and retries in case the version.txt upload failed during release.

[sukantoraymond]

With this PR, no more checking google for version number. It will all come from version.txt in flow cli repo

[devbugging]

Have you tested this out manually?

[sukantoraymond]

Tested

Raymonds-MBP-3:flow-cli raymondsukanto$ sh install.sh
Downloading version v0.39.1 ...