FreeBSD web build failed on build-web.ysv.freebsd.org

[User Www-data]

===> doc/books/developers-handbook (all)
===> doc/books/faq (all)
===> doc/books/fdp-primer (all)
===> doc/books/handbook (all)
===> doc/books/pmake (all)
===> doc/books/porters-handbook (all)
Warning: dep file /usr/local/www/build/head/en_US.ISO8859-1/books/porters-handbook/uses.xml does not exist
Warning: dep file /usr/local/www/build/head/en_US.ISO8859-1/books/porters-handbook/versions.xml does not exist
===> ports
--- all ---
cd /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports;  make  -j 8 -J 15,16 .MAKE.LEVEL.ENV=MAKELEVEL DIRPRFX=ports/ -f /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports/Makefile.inc0 all
cd growth;  make  -j 8 -J 15,16 .MAKE.LEVEL.ENV=MAKELEVEL DIRPRFX=ports/ all
--- all ---
cd /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports/growth/../../../../share/tools/portsgrowth;  make  -j 8 -J 15,16 -j 8 -J 15,16 .MAKE.LEVEL.ENV=MAKELEVEL DIRPRFX=ports/ all
--- status.png ---
/usr/local/bin/gnuplot ports.plt

set terminal png
             ^
"ports.plt", line 2: unknown or ambiguous terminal type; type just 'set terminal' for a list

*** [status.png] Error code 1

make[3]: stopped in /usr/local/www/build/head/share/tools/portsgrowth
1 error

make[3]: stopped in /usr/local/www/build/head/share/tools/portsgrowth
*** [all] Error code 2

make[2]: stopped in /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports/growth
1 error

make[2]: stopped in /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports/growth
*** [all] Error code 2

make[1]: stopped in /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports
1 error

make[1]: stopped in /usr/local/www/build/head/en_US.ISO8859-1/htdocs/ports
*** [all] Error code 2

make: stopped in /usr/local/www/build/head/en_US.ISO8859-1/htdocs
1 error

make: stopped in /usr/local/www/build/head/en_US.ISO8859-1/htdocs
        5.16 real         2.10 user         3.67 sys

latestrevision.timestamp "2018-01-14 08:03:04" 
latestrevision.committer "ryusuke"		
latestrevision.number "51384"