fix: wrong npm doctor command result

[vanishcode]

Detail

when I run npm doctor, I found that the some infomation in the result table were totaly wrong, look the screenshot:

look at the Recommendation column

the right result:

I found that if I changed the default registry to another url (such as https://registry.npm.taobao.org), and ping returns error, it would happend.

so i checked and modified the check-ping.js, when ping is failed, return cb(null, [err.code.substr(1), 'failed']) instead of cb(null, [err.code.substr(1)])

i don't know if it's a bug certainty, if it's realy not, i'll close this pr.

(forgive me that English is not my mother language······)

Environment

macOS 10.15.5
node 10.18.0
npm 6.14.5 (from source code)

[ruyadorno]

hi @vanishcode thanks for the contribution 😊 this looks like a good fix! we would need some unit tests that could help us reproduce the error and that we can use it to validate the fix solves it - you can take a look at https://github.com/npm/cli/blob/latest/test/tap/doctor.js for reference (and that would also be the perfect place to add a new test).

[vanishcode]

ok, I will add unit test for this fix later. thank you! @ruyadorno

[ruyadorno]

Thanks! This looks great 😄