[Fix] `nvm_strip_path`: Preserve leading/trailing colons #1083

Job	Run time
shellcheck_matrix (bash, nvm.sh)	46s
shellcheck_matrix (sh, nvm.sh)	41s
shellcheck_matrix (dash, nvm.sh)	47s
shellcheck_matrix (ksh, nvm.sh)	42s
shellcheck_matrix (bash, install.sh)	28s
shellcheck_matrix (bash, bash_completion)	24s
shellcheck_matrix (bash, nvm-exec)	25s
shellcheck	7s
	4m 20s

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