[Fix] `nvm_get_arch`: proper value for alpine linux #1116

Job	Run time
shellcheck_matrix (bash, nvm.sh)	51s
shellcheck_matrix (sh, nvm.sh)	45s
shellcheck_matrix (dash, nvm.sh)	1m 2s
shellcheck_matrix (ksh, nvm.sh)	55s
shellcheck_matrix (bash, install.sh)	39s
shellcheck_matrix (bash, bash_completion)	26s
shellcheck_matrix (bash, nvm-exec)	33s
shellcheck	6s
	5m 17s

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