pgroonga: Bump pgroonga version to 2.2.8 when building from source.
pgroonga: Bump pgroonga version to 2.2.8 when building from source.

hackerkid/zulip,andersk/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,punchagan/zulip,andersk/zulip,punchagan/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,kou/zulip,kou/zulip,andersk/zulip,andersk/zulip,rht/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,hackerkid/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,kou/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,rht/zulip