Fix each

[chihiro-adachi]

When running in the environment of php 7.2, the following warning was issued.
The each() function is deprecated. This message will be suppressed on further calls: 1x

each() function seems to be deprecated in 7.2.
http://php.net/manual/en/function.each.php

I tried to fix it, please merge if necessary.

[nrk]

In the end I fixed it by simply using key() and current() (see 157f658), painless fix as there was no real need for using each() to begin with. Thank you anyway @chihiro-adachi for reporting this! By the way, the next time please do not mix commits with different scopes in a PR (that is, the fix that removed each() and the change targeting TravisCI), two separate PRs even if tiny are way better.

[chihiro-adachi]

thank you 😄