[Fix] `nvm_get_arch`: proper value for alpine linux #1126

Job	Run time
shellcheck_matrix (bash, nvm.sh)	54s
shellcheck_matrix (sh, nvm.sh)	58s
shellcheck_matrix (dash, nvm.sh)	48s
shellcheck_matrix (ksh, nvm.sh)	39s
shellcheck_matrix (bash, install.sh)	30s
shellcheck_matrix (bash, bash_completion)	30s
shellcheck_matrix (bash, nvm-exec)	34s
shellcheck	7s
	5m 0s

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