Updated copyright notices to include the year 2018.

doc/man/doveadm-sieve.1.in

doc/man/pigeonhole.7.in

doc/man/sieve-dump.1.in

doc/man/sieve-filter.1.in

doc/man/sieve-test.1.in

doc/man/sievec.1.in

src/lib-managesieve/managesieve-arg.c

src/lib-managesieve/managesieve-arg.h

src/lib-managesieve/managesieve-parser.c

src/lib-managesieve/managesieve-parser.h

src/lib-managesieve/managesieve-quote.c

src/lib-managesieve/managesieve-quote.h

src/lib-sieve-tool/mail-raw.c

src/lib-sieve-tool/mail-raw.h

src/lib-sieve-tool/sieve-tool.c

src/lib-sieve-tool/sieve-tool.h

src/lib-sieve/cmd-discard.c

src/lib-sieve/cmd-if.c

src/lib-sieve/cmd-keep.c

src/lib-sieve/cmd-redirect.c