ngx-releng: add \t check

[chensunny]

Brackground

While I PR to the openresty/lua-nginx-module#2412, it will run the check like this:

before_install:
  - '! grep -n -P ''(?<=.{80}).+'' --color `find src -name ''*.c''` `find . -name ''*.h''` || (echo "ERROR: Found C source lines exceeding 80 columns." > /dev/stderr; exit 1)'
  - '! grep -n -P ''\t+'' --color `find src -name ''*.c''` `find . -name ''*.h''` || (echo "ERROR: Cannot use tabs." > /dev/stderr; exit 1)'
  - /usr/bin/env perl $(command -v cpanm) --sudo --notest Test::Nginx IPC::Run > build.log 2>&1 || (cat build.log && exit 1)

https://app.travis-ci.com/github/openresty/lua-nginx-module/jobs/632424434

Key Change

• Add \t check for $cfiles $hfiles
• Add 80 length code limitation to $cfiles $hfiles