[Fix] `nvm_get_arch`: proper value for alpine linux #1127

Job	Run time
shellcheck_matrix (bash, nvm.sh)	46s
shellcheck_matrix (sh, nvm.sh)	40s
shellcheck_matrix (dash, nvm.sh)	42s
shellcheck_matrix (ksh, nvm.sh)	50s
shellcheck_matrix (bash, install.sh)	18s
shellcheck_matrix (bash, bash_completion)	26s
shellcheck_matrix (bash, nvm-exec)	28s
shellcheck	8s
	4m 18s

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