Server postgres_fdw "fetch_size" option cannot be updated

Hi everyone,

I'm playing around with postgres_fdw (version 1.0), and ran into an issue where I wanted to update the "fetch_size" option on the server level:

sql> CREATE SERVER test_remote FOREIGN DATA WRAPPER postgres_fdw OPTIONS (host 'postgres2', dbname 'test', updatable 'false')
[2017-12-28 10:30:13] completed in 35ms
sql> ALTER SERVER test_remote OPTIONS (set fetch_size '50')
[2017-12-28 10:30:26] [42704] ERROR: option "fetch_size" not found

However, I am able to properly set the "fetch_size" when originally defining the server:

sql> CREATE SERVER test_remote2 FOREIGN DATA WRAPPER postgres_fdw OPTIONS (host 'postgres2', dbname 'test', updatable 'false', fetch_size '50')
[2017-12-28 10:31:26] completed in 24ms


Both the local and remote servers are running the same version of postgres:

PostgreSQL 9.6.6 on x86_64-pc-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit