Fix build error on macOS

[minsoochoo0122_proton.me]

Summary

ruby is not manually added to /usr/local/bin since there is already pre-installed ruby (old version used by Apple) in that directory. On macOS, we need to manually add it by passing RUBY_CMD.
With Homebrew, Hugo 0.115 will be installed so we don't need the tip for "Hugo 0.90 and above" anymore.
LOCALBASE is not needed anymore on macOS.

Test Plan

bmake run USE_RUBYGEMS=YES RUBY_CMD=$(brew --prefix ruby)/bin/ruby

[minsoochoo0122_proton.me]

Restore ruby bin path