[Fix] nvm_download: send a well-formed Authorization header on the wget path

The wget path passed `NVM_AUTH_HEADER` as the raw header line
(e.g. `--header "Bearer secret-token"`),
omitting the `Authorization:` header name that the curl path includes.
Per the documented usage
(`NVM_AUTH_HEADER="Bearer secret-token"`) the value is the credential,
so wget was sending a malformed header.
Prefix it with `Authorization: ` to match the curl path.

nvm.sh

@@ -151,7 +151,7 @@ nvm_download() {
 
     if [ -n "${NVM_AUTH_HEADER:-}" ]; then
       sanitized_header=$(nvm_sanitize_auth_header "${NVM_AUTH_HEADER}")
-      ARGS="${ARGS} --header \"${sanitized_header}\""
+      ARGS="${ARGS} --header \"Authorization: ${sanitized_header}\""
     fi
     # shellcheck disable=SC2086
     eval wget $ARGS