tests: use the specified perl to execute cpanm. (#2157)

Author: xiaocang

.travis.yml

@@ -64,8 +64,7 @@ before_install:
  - sudo apt install --only-upgrade ca-certificates
  - '! 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)'
- - sudo cpanm --notest Test::Nginx IPC::Run > build.log 2>&1 || (cat build.log && exit 1)
-
+ - /usr/bin/env perl $(command -v cpanm) --sudo --notest Test::Nginx IPC::Run > build.log 2>&1 || (cat build.log && exit 1)
 install:
  - if [ ! -f download-cache/drizzle7-$DRIZZLE_VER.tar.gz ]; then wget -P download-cache http://openresty.org/download/drizzle7-$DRIZZLE_VER.tar.gz; fi
  - if [ ! -f download-cache/pcre-$PCRE_VER.tar.gz ]; then wget -P download-cache https://downloads.sourceforge.net/project/pcre/pcre/${PCRE_VER}/pcre-${PCRE_VER}.tar.gz; fi
@@ -143,4 +142,4 @@ script:
  - dig +short myip.opendns.com @resolver1.opendns.com || exit 0
  - dig +short @$TEST_NGINX_RESOLVER openresty.org || exit 0
  - dig +short @$TEST_NGINX_RESOLVER agentzh.org || exit 0
- - prove -I. -Itest-nginx/lib -r t/
+ - /usr/bin/env perl $(command -v prove) -I. -Itest-nginx/lib -r t/