Changed arch with uname for finding the architecture in macOS

[dastergon]

Description of the change:
Updated the arch command with uname for more accurate architecture identification.

Motivation for the change:
The arch command in macOS due to legacy reasons reports whether the Intel arches are capable of 32-bit.

For example, in my MBP 16" (Intel):

$ arch
i386
$ uname -m
x86_64

Consequently, the snippet for downloading operator-sdk manually. That's why I chose uname -m as a replacement.

Checklist
If the pull request includes user-facing changes, extra documentation is required:

• Add or update relevant sections of the docs website in website/content/en/docs

PTAL

[estroz]

/lgtm