[Fix] sanitize `NVM_AUTH_HEADER` in `wget` path #595

Job	Run time
tests (sourcing, zsh)	1m 14s
tests (install_script, bash)	1m 29s
tests (installation_iojs, dash)	1m 9s
tests (slow, zsh)	4m 0s
tests (slow, sh)	3m 22s
tests (installation_iojs, sh)	1m 8s
tests (installation_iojs, zsh)	1m 26s
tests (installation_iojs, bash)	1m 7s
tests (slow, dash)	3m 18s
tests (sourcing, bash)	57s
tests (sourcing, sh)	51s
tests (slow, bash)	3m 31s
tests (sourcing, dash)	52s
all test suites, all shells	4s
	24m 28s

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